Short answer
No one buys Paradise with deeds, not even the Prophet (ﷺ). A Muslim is saved by faith, by the good deeds that grow from it, and in the end by God's (﷾) mercy. A person becomes a Muslim by believing in the One God (﷾) and in Muhammad (ﷺ) as His Messenger. The Qur'an promises Paradise to "those who believe and work righteousness", and it names belief first. The Prophet (ﷺ) said that a Muslim who dies believing there is no god but Allah (﷾) will enter Paradise. Yet he also said that no one's deeds will save him unless God (﷾) covers him with mercy. God (﷾) forgives any sin He wills, except worshipping others beside Him if a person dies still doing it. Whoever turns away from it before death is forgiven. No priest stands in between, because God (﷾) is nearer to each person than the vein in his neck.
Full explanation
Faith comes first
Islam is the religion God (﷾) accepts, and a person enters it by faith, not by a deed. Verse after verse, the Qur'an promises reward to "those who believe and work righteousness". It names belief before deeds. Where a verse names deeds first, it still makes faith the condition: "and have faith, they will enter Heaven". Another verse says the believers are successful, and only then names their prayer. Good deeds grow out of faith. They do not replace it. Without faith, deeds are not accepted at all: the Qur'an says any religion other than Islam will never be accepted.
“The Religion before Allah is Islam (submission to His Will): Nor did the People of the Book dissent therefrom except through envy of each other, after knowledge had come to them. But if any deny the Signs of Allah, Allah is swift in calling to account.”
“But give glad tidings to those who believe and work righteousness, that their portion is Gardens, beneath which rivers flow. Every time they are fed with fruits therefrom, they say: "Why, this is what we were fed with before," for they are given things in similitude; and they have therein companions pure (and holy); and they abide therein (for ever).”
“Nay,-whoever submits His whole self to Allah and is a doer of good,- He will get his reward with his Lord; on such shall be no fear, nor shall they grieve.”
“If any do deeds of righteousness,- be they male or female - and have faith, they will enter Heaven, and not the least injustice will be done to them.”
“The believers must (eventually) win through,- Those who humble themselves in their prayers;”
“If anyone desires a religion other than Islam (submission to Allah), never will it be accepted of him; and in the Hereafter He will be in the ranks of those who have lost (All spiritual good).”
The weight of "no god but Allah"
Tawhid (the oneness of God (﷾)) weighs more than any other deed. The Prophet (ﷺ) said that whoever of his community dies still believing there is no god but Allah (﷾) will enter Paradise. Abu Dharr, one of his Companions, was astonished. He asked: even if he had committed adultery and theft? The Prophet (ﷺ) answered: even if he had. This does not make sin light. Al-Bukhari, who collected hadith in the ninth century, explains it as the one who repents before death. Hadith are reports of what the Prophet (ﷺ) said and did. Muslim scholars add that a believer who dies with sins unrepented may answer for them, but is not shut out of Paradise for ever. The Prophet (ﷺ) said that a person who says there is no god but Allah (﷾) will be brought out of the Fire. This is so if he has even a barley grain's weight of good in his heart.
Abu Dharr reports that the Prophet (ﷺ) said that anyone who says there is no god but Allah, and dies holding to it, will enter Paradise. Abu Dharr asked: even if he had committed adultery and theft? The Prophet said: even so, and repeated it each time Abu Dharr asked again. Al-Bukhari adds that this concerns the one who, at death or before it, repents and says there is no god but Allah: he is forgiven.
Abu Dharr reports that the Prophet (ﷺ) said Gabriel brought him the good news that whoever of his community dies without associating anything with Allah will enter Paradise. Abu Dharr asked: even if he committed adultery and theft? The Prophet said: even if he committed adultery and theft.
Anas reports that the Prophet (ﷺ) said: whoever says there is no god but Allah and has in his heart good the weight of a barley grain will be taken out of Hell; so too whoever has the weight of a wheat grain, and whoever has the weight of an atom.
Deeds do not buy Paradise
The Prophet (ﷺ) said that no one's deeds will save him. He was asked whether that was true even of him. He said yes, unless Allah (﷾) covers him with mercy. He taught that deeds are weighed by the intention behind them. And he told a man that he would be with those he loved. The man had little prayer and fasting to show, but he loved Allah (﷾) and His Messenger. Paradise is entered by God's (﷾) mercy. Faith and good deeds are how a servant seeks it. The Qur'an tells the believers to enter the Garden 'because of (the good) which ye did'. Muslim scholars explain that deeds are the means God (﷾) uses to grant His mercy, not a price that buys Paradise. The Prophet's (ﷺ) words about his own deeds show that mercy, not deeds, decides.
Abu Hurayra reports that the Prophet (ﷺ) said no one's deeds will save him. Asked whether that included him, he said: not even me, unless Allah covers me with His mercy. He then told them to do good deeds properly, sincerely and in moderation.
Umar ibn al-Khattab heard the Prophet (ﷺ) say that deeds are judged by their intentions, and each person receives what he intended. A man who emigrated for worldly gain or to marry a woman has only what he emigrated for.
Anas ibn Malik reports that a man asked the Prophet (ﷺ) when the Hour would come. The Prophet asked what he had prepared for it. The man said he had not prepared much prayer, fasting or charity, but he loved Allah and His Messenger. The Prophet told him he would be with those he loved.
“(Namely) those whose lives the angels take in a state of purity, saying (to them), "Peace be on you; enter ye the Garden, because of (the good) which ye did (in the world)."”
What God (﷾) forgives
The Qur'an states that God (﷾) forgives any sin to whom He wills, except associating partners with Him. That means worshipping others beside Him, called shirk. Muslim scholars read it as the person who dies still doing it. Another verse tells every sinner not to despair of God's (﷾) mercy, for He forgives all sins. Muslim scholars read it as a promise to the one who repents, as the next verse calls people to turn back to Him.
“Allah forgiveth not that partners should be set up with Him; but He forgiveth anything else, to whom He pleaseth; to set up partners with Allah is to devise a sin Most heinous indeed.”
“Say: "O my Servants who have transgressed against their souls! Despair not of the Mercy of Allah: for Allah forgives all sins: for He is Oft-Forgiving, Most Merciful.”
Believe in the one God (﷾), and that Muhammad (ﷺ) is His messenger. This is Islam, the religion God (﷾) accepts.
Do good, sincerely for God (﷾). Each deed counts by the intention behind it.
Sins along the way?
Turn back to God (﷾) and ask His forgiveness. He forgives every sin of those who repent.
The one exception: if a person dies still worshipping others beside God (﷾), or rejecting Him and His messenger after the message has reached them, that is not forgiven. God (﷾) punishes no one until a messenger has come to them.
Paradise is God's (﷾) gift: everyone who enters it enters by His mercy. No one earns it by good deeds alone, and the Prophet (ﷺ) humbly said this of himself too.
Paradise: gardens with rivers flowing beneath, a home forever.
No one stands between
There is no priest, no sacrament (a church rite said to give God's (﷾) grace) and no go-between. The Qur'an says God (﷾) is nearer to a person than his jugular vein (the large vein in the neck). It says He answers everyone who calls on Him.
“It was We Who created man, and We know what dark suggestions his soul makes to him: for We are nearer to him than (his) jugular vein.”
“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.”
A just reckoning
Every deed is seen: an atom's weight of good, and an atom's weight of evil. No one is punished for a message that never reached him, because God (﷾) does not punish until He has sent a messenger. And God (﷾) sent a messenger to every people, so no nation was left without guidance.
“Then shall anyone who has done an atom's weight of good, see it! And anyone who has done an atom's weight of evil, shall see it.”
“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).”
“For We assuredly sent amongst every People a messenger, (with the Command), "Serve Allah, and eschew Evil": of the People were some whom Allah guided, and some on whom error became inevitably (established). So travel through the earth, and see what was the end of those who denied (the Truth).”
“Verily We have sent thee in truth, as a bearer of glad tidings, and as a warner: and there never was a people, without a warner having lived among them (in the past).”
The Christian claim
Christians often say that Christianity teaches salvation as a free gift received by faith, while Islam makes people earn it. They point to Paul's letter to the Ephesians. Paul was a Christian missionary of the first century. The letter says people are saved by grace (God's (﷾) free favour) through faith, not of works.
“For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast.”
Where the New Testament divides
Paul says a man is justified (declared right with God (﷾)) by faith without the deeds of the law. James says a man is justified by works, and not by faith only. Both stand in the New Testament. Ezekiel, a prophet of the sixth century BCE, says the wicked man who turns from his sins and does what is right shall live. He names no sacrifice as the condition. Jesus quoted God (﷾): "I will have mercy, and not sacrifice." And the book of Acts says there is no other name by which people can be saved. Read strictly, as many Christians read it, that shuts out everyone who died without hearing that name.
“Therefore we conclude that a man is justified by faith without the deeds of the law.”
“Ye see then how that by works a man is justified, and not by faith only.”
“But if the wicked will turn from all his sins that he hath committed, and keep all my statutes, and do that which is lawful and right, he shall surely live, he shall not die. All his transgressions that he hath committed, they shall not be mentioned unto him: in his righteousness that he hath done he shall live.”
“But go ye and learn what that meaneth, I will have mercy, and not sacrifice: for I am not come to call the righteous, but sinners to repentance.”
“Neither is there salvation in any other: for there is none other name under heaven given among men, whereby we must be saved.”
Verse by verse
Ephesians 2:8-9 — Epistle to the Ephesians, chapter 2, verses 8-9
“For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast.”
Cited for
Salvation is a gift received by faith, while Islam teaches that a person must earn Paradise by works.
The response
Islam does not teach that. The Prophet (ﷺ) said that no one, not even he, is saved by his deeds without God's (﷾) mercy. The Qur'an does speak of deeds being weighed. But God (﷾) multiplies each good deed tenfold and counts each evil only as one (6:160). Faith is the condition for any deed to count at all. And the New Testament itself is divided: James says a man is justified by works and not by faith only.
Where it lands — Islam grounds salvation in faith and God's (﷾) mercy, so the charge of "earning" Paradise misreads it.
Acts 4:12 — Acts of the Apostles, chapter 4, verse 12
“Neither is there salvation in any other: for there is none other name under heaven given among men, whereby we must be saved.”
Cited for
Salvation comes only through the name of Jesus.
The response
Read strictly, that shuts out everyone who died without hearing the name of Jesus. Ezekiel says God (﷾) forgives the wicked man who turns from his sins, and names no sacrifice. Jesus quoted God's (﷾) words: "I will have mercy, and not sacrifice". The Qur'an adds that God (﷾) punishes no one until a messenger has reached him.
Where it lands — Ezekiel, and the words Jesus quoted, describe a God who forgives the one who repents, which is what the Qur'an teaches.
Qur'an 19:60-61 — Surat Maryam (Mary), verses 60-61
“Except those who repent and believe, and work righteousness: for these will enter the Garden and will not be wronged in the least,- Gardens of Eternity, those which (Allah) Most Gracious has promised to His servants in the Unseen: for His promise must (necessarily) come to pass.”
Cited for
A Christian can be sure of salvation, but a Muslim never knows whether he will go to Paradise.
The response
The Qur'an promises the Garden to those who repent, believe and do good, and says His promise must come to pass. A Muslim is sure of that promise. What he does not presume is his own end, so he asks God (﷾) to keep his heart firm, as the Prophet (ﷺ) prayed: O Turner of the hearts, turn our hearts to Your obedience. Christians are not agreed on this either. The Catholic Council of Trent condemned anyone who claims infallible certainty that he will persevere to the end. Jesus said that not every one who says to him "Lord, Lord" will enter the kingdom.
Where it lands — Islam promises Paradise to those who believe and do good. Certainty of one's own end is not claimed by Islam, nor by much of the church.
Perspectives
Mainstream Christian
Salvation is God's free gift, received by faith in Christ's death and resurrection, and it cannot be earned by works.
Ephesians says believers are saved by grace through faith, not of works.
Rebuttal
Islam agrees that no one earns Paradise: the Prophet (ﷺ) said no one is saved by his deeds without God's (﷾) mercy. Islam also makes faith the condition for any deed to count. And James says a man is justified by works and not by faith only.
Acts says salvation is found in no other name than that of Jesus.
Rebuttal
Grant that Acts says this, but asked how to enter life, Jesus himself said: keep the commandments. Ezekiel says God (﷾) forgives the sinner who repents, naming no sacrifice, and Jesus quoted God (﷾): "I will have mercy, and not sacrifice". The Qur'an adds that God (﷾) punishes no one until a messenger has reached him.
The Islamic perspective
Salvation comes by faith in the One God (﷾) and His Messenger (ﷺ), shown in good deeds, and granted in the end by God's (﷾) mercy. Nobody earns it, and nobody stands between a person and God (﷾).
The Qur'an promises Paradise to those who believe and do good, naming belief first.
The Prophet (ﷺ) said that whoever of his community dies believing there is no god but Allah (﷾) will enter Paradise. He said this even of one who had committed adultery and theft.
The Prophet (ﷺ) taught that no one's deeds will save him, not even his own, without God's (﷾) mercy.
Deeds are judged by the intention behind them.
God (﷾) forgives any sin He wills except associating partners with Him. Even that He forgives to the one who repents.
No one is punished for a message that never reached him.
God (﷾) is near and answers directly, so no priest or mediator is needed.