Short answer
God (﷾) has made Himself known, but He has not forced Himself on anyone. Islam teaches that life is a test, and a test of trust needs some things unseen. If He appeared beyond all doubt, that test would be over. The signs are open to anyone who looks, and the Qur'an promises that more will be shown. The door to Him is open to anyone who turns, even by a small step. Guidance is promised to those who strive in God's (﷾) cause. No one is punished before the message has reached him. So the delay is not a trick. It is time to look, to think and to answer freely. This page does not say that every person who doubts is resisting.
Full explanation
The question, stated at its strongest
The philosopher J. L. Schellenberg gave this question its best-known form, first in 1993 and in its current form in 2015. He argues that a perfectly loving God (﷾) would always be open to a close relationship with every person able to have one. Then no one who is not resisting would be without belief. He holds that some people are in that position, so he concludes that there is no such God (﷾). This is not the claim that doubters are insincere. It is the claim that some honest people still do not find God (﷾). The answers below meet it on its own terms.
Argues that a perfectly loving God would make a personal relationship with Himself available to every person capable of one, so that no such person would fail to believe through no fault of his own. He holds that such blameless non-belief occurs, and concludes that there is no such God. In later books (The Wisdom to Doubt, 2007; The Hiddenness Argument, 2015) he restates it: a perfectly loving God would always be open to such a relationship, so no one would be without belief who is not resisting.
Islam's answer: the door is open to anyone who turns
Schellenberg does not ask for an angel. He asks only that a relationship with God (﷾) be open to anyone who is not resisting. Islam says it is. In a saying the Prophet (ﷺ) reported from God (﷾), whoever comes a hand-span nearer, God (﷾) comes an arm's length nearer. Whoever comes walking, God (﷾) comes to him running (Bukhari 7405). The Qur'an says God (﷾) is close and answers the one who calls (2:186). A person who is unsure can still turn and ask, in his own words, to be shown the truth. What a person seeks and does is the test (67:2). Islam does not read any heart from outside, and it does not say that a person's present unbelief means he has not turned.
The Prophet (ﷺ) reports that Allah says: I am as My servant thinks of Me, and I am with him when he remembers Me; if he comes a hand-span nearer to Me, I come an arm's length nearer to him, and if he comes to Me walking, I go to him running. Also in Sahih Muslim 2675.
“When My servants ask thee concerning Me, I am indeed close (to them): I listen to the prayer of every suppliant when he calleth on Me: Let them also, with a will, Listen to My call, and believe in Me: That they may walk in the right way.”
“He Who created Death and Life, that He may try which of you is best in deed: and He is the Exalted in Might, Oft-Forgiving;-”
Unseen is not the same as unknowable
Most of what anyone knows well is not seen. No one has seen another person's mind, and no one can go back and watch the past. We know them by what they leave behind. A Maker who depends on nothing would not be one more thing in the world that could stand in front of us. In this life we should expect to know Him by His works, not by sight. The reasons from those works are open to every reader. They are set out on the pages about how we know God (﷾) exists and who created God (﷾). The Qur'an asks the reader to look at what exists in the same way.
“Were they created of nothing, or were they themselves the creators? Or did they create the heavens and the earth? Nay, they have no firm belief.”
Islam's answer: a test needs some things unseen
Islam gives the first reason for the delay: this life is a test. God (﷾) made death and life to try which of us is best in deed (67:2). Faith that rests on reasons and trust still leaves a person free. Every day he chooses whether to act on it, and that choice is the test (29:2-3). The Qur'an praises those who believe in the unseen, and in the same verse it names prayer and giving (2:3). Belief, worship and conduct belong together. Sight that leaves no room for doubt would not end the choosing. It would end the trust in the unseen, and the Qur'an says it would end the time given (6:8).
“He Who created Death and Life, that He may try which of you is best in deed: and He is the Exalted in Might, Oft-Forgiving;-”
“Who believe in the Unseen, are steadfast in prayer, and spend out of what We have provided for them;”
“Do men think that they will be left alone on saying, "We believe", and that they will not be tested? We did test those before them, and Allah will certainly know those who are true from those who are false.”
Why God (﷾) does not simply show Himself beyond doubt
This is the common form of the question. Schellenberg's is different, as the first block shows. The Qur'an records the demand: why was no angel sent down? Its answer is that if an angel were sent, the matter would be settled at once, with no more time given (6:8). Al-Tabari reads this as no time left to turn back in repentance. Al-Qurtubi reports Ibn Abbas saying that people could not bear to see an angel in his true form. The next verse adds that an angel would have been sent as a man. The confusion would remain (6:9). So the delay is a mercy. It is time to look, to think and to turn. Faith that begins only when sight leaves no choice is not the faith that was asked for. The Qur'an says the same of the day when the last signs come: belief that begins then does not help (6:158). Ibn Kathir places that day at the end of the world.
“They say: "Why is not an angel sent down to him?" If we did send down an angel, the matter would be settled at once, and no respite would be granted them. If We had made it an angel, We should have sent him as a man, and We should certainly have caused them confusion in a matter which they have already covered with confusion.”
Reads the demand "why is no angel sent down" as the unbelievers asking for an angel from heaven, in the angel's own form, to confirm the Prophet (ﷺ). Reads "the matter would be settled" as: if God sent the angel they asked for and they still disbelieved, the punishment would come at once. They would be given no time to turn back in repentance, as happened to earlier peoples who asked for signs and then rejected them. He also reports Mujahid and Ikrima reading it as the Hour itself arriving.
Gives several readings of "the matter would be settled". Ibn Abbas: if they saw the angel in his true form they would die, because they could not bear to look at him. Mujahid and Ikrima: the Hour would come. Al-Hasan and Qatada: they would be destroyed at once, because God's way is that whoever asks for a sign, is shown it and does not believe, is destroyed then. He explains "no respite" as: they would be given neither time nor delay.
“Are they waiting to see if the angels come to them, or thy Lord (Himself), or certain of the signs of thy Lord! the day that certain of the signs of thy Lord do come, no good will it do to a soul to believe in them then if it believed not before nor earned righteousness through its faith. Say: "Wait ye: we too are waiting."”
Reads the waiting for the angels, for the Lord to come, or for some of His signs as what awaits the unbelievers on the Day of Resurrection, and in the signs that come before it. For those signs he cites Abu Hurayra's report in Sahih al-Bukhari that the Hour will not come until the sun rises from the west. When people see it all on earth will believe, and that is when belief does a soul no good if it did not believe before. He notes that Muslim also reports it.
What is given instead: signs, a promise and an open door
The Qur'an says: "Soon will We show them our Signs" out in the world and in their own souls (41:53). The wording is future. Signs keep coming, and no one has seen them all. Messengers came so that no one would have a plea against God (4:165). No one is punished before a message has reached him (17:15). Guidance is promised to those who strive in God's (﷾) cause (29:69). Al-Qurtubi gathers readings of this verse that take the striving widely, including acting on the good one already knows. Islam does not say that every person who doubts is resisting. It leaves each heart to God (﷾).
“Soon will We show them our Signs in the (furthest) regions (of the earth), and in their own souls, until it becomes manifest to them that this is the Truth. Is it not enough that thy Lord doth witness all things?”
“Messengers who gave good news as well as warning, that mankind, after (the coming) of the messengers, should have no plea against Allah: For Allah is Exalted in Power, Wise.”
“Who receiveth guidance, receiveth it for his own benefit: who goeth astray doth so to his own loss: No bearer of burdens can bear the burden of another: nor would We visit with Our Wrath until We had sent a messenger (to give warning).”
“And those who strive in Our (cause),- We will certainly guide them to our Paths: For verily Allah is with those who do right.”
Collects several readings of "those who strive in Our cause". Al-Suddi and others say the verse came down before fighting was prescribed, and Ibn Atiyya draws from this that it means a general striving in God's religion and for His good pleasure. Ibn Abbas and Ibrahim ibn Adham read it of those who act on what they know. Abu Sulayman al-Darani includes striving against one's own self in obedience.
The replies answered
Divine Hiddenness and Human Reason (1993)
Argues that a perfectly loving God would make a personal relationship with Himself available to every person capable of one, so that no such person would fail to believe through no fault of his own. He holds that such blameless non-belief occurs, and concludes that there is no such God. In later books (The Wisdom to Doubt, 2007; The Hiddenness Argument, 2015) he restates it: a perfectly loving God would always be open to such a relationship, so no one would be without belief who is not resisting.
Cited for
A perfectly loving God would never leave anyone who is not resisting without a relationship to Him. Honest non-belief exists. So no such God exists.
The response
The premise asks that a relationship be open to anyone who is not resisting. Islam says it is: God (﷾) comes nearer to whoever turns to Him, however little (Bukhari 7405). Honest non-belief is real, and nothing here denies it. The present state of a person's belief is not the final verdict. No one is punished before the message reaches him (17:15), and guidance is promised to those who strive (29:69). The Qur'an does not call every doubter a resister.
Where it lands — Honest non-belief does not show that God (﷾) is absent. It fits a life that is a test with the door still open. Nothing here calls an honest seeker a liar, and Islam leaves each heart to God (﷾).
Qur'an 6:8-9 — Surat al-An'am (The Cattle), verses 8-9
“They say: "Why is not an angel sent down to him?" If we did send down an angel, the matter would be settled at once, and no respite would be granted them. If We had made it an angel, We should have sent him as a man, and We should certainly have caused them confusion in a matter which they have already covered with confusion.”
Cited for
If God wanted belief, He could send an angel, and everyone would believe.
The response
The Qur'an records this very demand and answers it. An angel sent as asked would end the matter at once, with no more time given (6:8). Al-Tabari reads that as no time left to repent. Time to look, think and turn is what the delay gives. God (﷾) did send messengers who were human, with signs and a book that can still be tested.
Where it lands — The demand would end the time given for a free answer. The Qur'an offers messengers and signs in its place.
Qur'an 29:2-3 — Surat al-'Ankabut (The Spider), verses 2-3
“Do men think that they will be left alone on saying, "We believe", and that they will not be tested? We did test those before them, and Allah will certainly know those who are true from those who are false.”
Cited for
An all-knowing God already knows who will believe. A test teaches Him nothing, so it is pointless.
The response
The test is not for God's (﷾) information. Al-Tabari reads "Allah will certainly know" as: God (﷾) knows before, during and after, and the test makes the truth of each person plain. Deeds are shown, and no one is left with a plea against God (4:165). Knowing what a person will choose is not forcing the choice.
Where it lands — The test shows people's choices in their deeds and removes every plea. It does not tell God (﷾) anything new.
Qur'an 6:158 — Surat al-An'am (The Cattle), verse 158
“Are they waiting to see if the angels come to them, or thy Lord (Himself), or certain of the signs of thy Lord! the day that certain of the signs of thy Lord do come, no good will it do to a soul to believe in them then if it believed not before nor earned righteousness through its faith. Say: "Wait ye: we too are waiting."”
Cited for
The Qur'an threatens people who wait for a sign. That is a threat, not an answer.
The response
Ibn Kathir reads the verse of the Day of Resurrection and the last signs before it. It describes a time after which belief that begins does not help. It does not speak of a person who asks honest questions now. The same book promises signs to come (41:53) and asks people to reflect (52:35-36).
Where it lands — The verse marks the end of the test. It does not punish anyone for asking.
Qur'an 2:3 — Surat al-Baqara (The Cow), verse 3
“Who believe in the Unseen, are steadfast in prayer, and spend out of what We have provided for them;”
Cited for
People who are certain God exists still do wrong, so clear evidence would leave freedom intact and hiddenness is not needed.
The response
Islam agrees that sight does not make anyone obey. What sight ends is the trust the Qur'an asks for, belief in the unseen (2:3), and the time left to answer (6:8-9). The test is about those two things.
Where it lands — The claim is true but does not touch what the test is about: trust before the matter is settled.
Qur'an 17:15 — Surat al-Isra (The Night Journey), verse 15
“Who receiveth guidance, receiveth it for his own benefit: who goeth astray doth so to his own loss: No bearer of burdens can bear the burden of another: nor would We visit with Our Wrath until We had sent a messenger (to give warning).”
Cited for
People believe what their birthplace taught them (Maitzen). A God who wanted all to know Him would not let belief depend on where one is born.
The response
Belief often does follow birthplace. But no one is punished before a messenger has come (17:15), and messengers were sent so that no one has a plea against God (4:165). God (﷾) alone judges what each person was given.
Where it lands — Where a person was born does not decide the verdict. The account depends on what reached him.
Perspectives
The argument from divine hiddenness
A perfectly loving God would always be open to a relationship with anyone able to have one. Yet some honest people do not believe, so there is no such God.
J. L. Schellenberg, Divine Hiddenness and Human Reason (1993), restated in 2007 and 2015
A perfectly loving God would always be open to a relationship with every capable person. Then no one who is not resisting would lack belief. Yet some people who are not resisting do not believe, so there is no such God.
Rebuttal
Grant that honest non-belief exists at a given time. Islam says the door is open to anyone who turns, even a hand-span (Bukhari 7405). Belief now is not the final verdict. Guidance is promised to those who strive (29:69), and no one is punished before the message reaches him (17:15).
The evidential arguments from non-belief
The way belief is spread across the world fits a world without God better than a God who wants everyone to know Him. Belief seems to follow where a person is born.
Stephen Maitzen, "Divine Hiddenness and the Demographics of Theism" (2006), and others
A God who wanted to be known would make the evidence clearer. That it is not clear is better explained if there is no God.
Rebuttal
Grant that belief is not forced on anyone. A life that is a test would look like this (2:3; 67:2), so unclear signs do not count against God (﷾). The reasons for a Maker are public and can be weighed.
Belief follows where a person is born, which a God who wanted everyone to know Him would not allow.
Rebuttal
Grant that belief often follows birthplace. No one is punished before a messenger has come (17:15), and messengers were sent so that no one has a plea against God (4:165). God (﷾) alone judges what each person was given.
Clear evidence would not remove free choice
People can be sure that God exists and still choose wrongly. So a test of character does not need God to stay hidden, and believing without sight is no virtue.
A general reply to the freedom answer, as discussed in the Stanford Encyclopedia of Philosophy
People who are sure that God exists still choose wrongly, so hiddenness is not needed to protect free choice.
Rebuttal
Islam agrees that sight does not force obedience. What clear sight ends is the test of trusting the unseen (2:3) and the time left to respond (6:8-9). That is what the Qur'an says the test is.
To believe without seeing is not a virtue, because belief ought to follow the evidence.
Rebuttal
Islam does not ask for belief without reasons. It tells people to look and to reason (41:53; 52:35-36). It holds that belief in the unseen (2:3) rests on those reasons and on the messengers, not on the eyes.
The Islamic perspective
Life is a test, and a test of trust needs some things unseen. God (﷾) gives signs, messengers and an open door to guidance, and no one is punished before the message reaches him.
Life is a test of which of us is best in deed. The Qur'an praises those who believe in the unseen.
Had an angel been sent down, the matter would have been settled at once. The commentators read this as the end of the time to turn back.
Belief that begins only when the last signs arrive does not benefit the soul. Faith forced by sight is not the faith that was asked for.
The Qur'an promises that signs will be shown out in the world and in people's own souls.
No one is punished before a message has reached him. Messengers were sent so that no one has a plea against God (﷾).
Guidance is promised to those who strive in God's (﷾) cause. The commentators read that striving widely, so the search is not closed to anyone still looking.