Short answer
The Trinity, the belief in one God in three persons, took shape at church councils centuries after Jesus. No prophet taught it. Islam teaches that Jesus, like every prophet, taught that God (﷾) is One. The New Testament gives Jesus high titles, but again and again it puts God (﷾) above him. Even a Jesuit historian who holds the doctrine says the New Testament gives no formulated doctrine of the Trinity. In 325 the Council of Nicaea declared the Son "of one substance" with the Father. The Emperor Constantine urged that word on the bishops. Church councils then argued the question for decades. In 380 the emperors ordered all their peoples to believe in the Trinity. In 381 the Council of Constantinople added that the Holy Spirit is worshipped with the Father and the Son. The Qur'an tells Christians plainly: say not "Trinity".
Full explanation
What Christians hold
Christians hold that the councils did not invent the Trinity. They say the councils put into words what the Church already believed. They point to Jesus' command to baptise in the name of the Father, and of the Son, and of the Holy Ghost (the Holy Spirit). They read the Creed of Nicaea, the statement of belief agreed there, as a faithful summary of Scripture. The record of the councils tells a different story.
“Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:”
The creed opens: "We believe in one God, the Father Almighty, maker of all things visible and invisible". The council confessed the Son as begotten of the Father, true God of true God, and "of one substance" (homoousios) with the Father, and condemned those who said there was a time when he was not.
What the early writers show
A new word proves nothing by itself. Muslims too use a later word, tawhid (God's (﷾) oneness), for what every prophet taught. What matters is whether the belief was taught. A Jesuit, a member of a Catholic religious order, has written a history of the doctrine and believes it. Even he writes that the New Testament gives no formulated doctrine of the Trinity. Tertullian, a Christian writer in North Africa, defended the Trinity. Even he admits that the simple, who always make up the majority of believers, were alarmed by it. The Catholic Encyclopedia of 1912 also defends the doctrine, yet it admits that Scripture has no single term naming the three together. The Greek word trias first appears in Theophilus, bishop of Antioch, about AD 180. His three are God (﷾), His Word and His Wisdom. The Latin trinitas first appears in Tertullian.
A Jesuit historian of the doctrine, himself a Trinitarian, writes that the New Testament writers give no formal or formulated doctrine of the Trinity and no explicit teaching that in one God there are three co-equal divine persons. He holds that they supply ideas from which the later doctrine was built.
Tertullian defends the doctrine he calls the Trinity (Latin trinitas), and admits that the simple, who always make up the majority of believers, are alarmed by it, fearing that it divides the one God.
A Catholic reference work that defends the doctrine states that Scripture has as yet no single term naming the three divine persons together; that the Greek word trias first appears in Theophilus of Antioch about AD 180; and that the Latin trinitas appears afterwards in Tertullian.
Theophilus calls God, his Word and his Wisdom a triad (Greek trias). It is the earliest known use of the term in Christian writing.
How councils and emperors settled it
At Nicaea in 325 the bishops declared the Son of one substance with the Father. Eusebius of Caesarea, a bishop and historian who was there, wrote that Constantine urged the word on them. The fifth-century church historian Socrates records that an edict of the emperor then sent Arius into exile. Arius was a priest who denied that the Son was equal to the Father. The fight went on for decades. In 357 a council at Sirmium banned the word substance and declared the Father greater than the Son. In 380 the emperors ordered every people under their rule to believe in the Trinity, and threatened all others as heretics. In 381 the Council of Constantinople expanded the creed's line on the Holy Spirit. It called Him Lord and giver of life, to be worshipped with the Father and the Son. R. P. C. Hanson, a historian of the early church, describes the years 318 to 381 as a search for a doctrine. He does not call them the defence of one already settled.
The creed opens: "We believe in one God, the Father Almighty, maker of all things visible and invisible". The council confessed the Son as begotten of the Father, true God of true God, and "of one substance" (homoousios) with the Father, and condemned those who said there was a time when he was not.
Eusebius, bishop of Caesarea, wrote to his church after the Council of Nicaea that the emperor Constantine urged all the bishops to agree to the creed with the insertion of the single word homoousios (of one substance), and explained the word himself. Socrates adds that five bishops at first objected to the word, and that an edict of the emperor sent Arius into exile.
A council of bishops at Sirmium in 357, opposed to the Nicene formula, thirty-two years after Nicaea, ruled that the word "substance" (ousia), and so the Nicene formula "of one substance", should not be used at all, because it is not contained in the divine Scriptures. It also declared that no one can doubt the Father is greater than the Son, quoting Jesus' words "He that sent me is greater than I".
Issued on 27 February 380. The emperors ordered all the peoples under their rule to follow the religion taught by the apostle Peter, and to believe in the one deity of the Father, the Son and the Holy Spirit, in equal majesty and a holy Trinity. Those who refused were to be branded heretics and to face divine punishment and then the emperors' own.
The council confessed the Holy Spirit as the Lord and Giver of life, who proceeds from the Father, and who with the Father and the Son together is worshipped and glorified.
A history of the Arian controversy from 318 to 381. Argues that it was not the defence of a settled orthodoxy against heresy, but a search in which the church's doctrine of God was worked out, and reached its final form only in 381.
- About AD 180
The Greek word appears
Theophilus of Antioch uses the Greek word trias, “a set of three”. His three are God (﷾), His Word and His Wisdom.
- Early 200s
The Latin word follows
Tertullian is the first to use the Latin word trinitas. He admits that most ordinary believers of his day were alarmed by it.
- 325
The Council of Nicaea
The bishops declare the Son “of one substance” with the Father. The Emperor Constantine urges that word on them, and an order of the emperor sends Arius, who taught that the Son had a beginning, into exile.
- 357
A council goes the other way
A council at Sirmium bans the word “substance” and declares the Father greater than the Son.
- 380–381
Made law by emperors
The emperors order all their peoples to believe in the Trinity. In 381 the Council of Constantinople adds to the creed that the Holy Spirit is worshipped with the Father and the Son.
The word Trinity is not in the Bible. The Qur'an tells Christians not to say “Trinity”, because Allah (﷾) is one.
How the confusion arose
The New Testament writers gave Jesus exalted titles. Revelation, the last book of the New Testament, has a speaker whom Christians take to be Jesus. He calls himself the first and the last, a title God takes in Isaiah. Later readers took the shared titles as a shared nature. But the same writers say who gave Jesus his rank. God (﷾) raised him and set him at His own right hand. God (﷾) exalted him and gave him a name. He obtained a better name by inheritance. And Paul, a Christian missionary of the first century, calls him "the firstborn of every creature".
“I am Alpha and Omega, the beginning and the end, the first and the last.”
“Thus saith the Lord the King of Israel, and his redeemer the Lord of hosts; I am the first, and I am the last; and beside me there is no God.”
“Which he wrought in Christ, when he raised him from the dead, and set him at his own right hand in the heavenly places, Far above all principality, and power, and might, and dominion, and every name that is named, not only in this world, but also in that which is to come:”
“Wherefore God also hath highly exalted him, and given him a name which is above every name:”
“Being made so much better than the angels, as he hath by inheritance obtained a more excellent name than they.”
“Who is the image of the invisible God, the firstborn of every creature:”
God (﷾) is above him in the New Testament
Again and again the New Testament puts God (﷾) above Jesus. The head of Christ is God. At the end the Son himself will be subject to God (﷾). Jesus says his Father is greater than he is. Hebrews, a New Testament letter, gives Jesus the highest titles. Even so, it speaks to him of "God, even thy God".
“But I would have you know, that the head of every man is Christ; and the head of the woman is the man; and the head of Christ is God.”
“And when all things shall be subdued unto him, then shall the Son also himself be subject unto him that put all things under him, that God may be all in all.”
“Ye have heard how I said unto you, I go away, and come again unto you. If ye loved me, ye would rejoice, because I said, I go unto the Father: for my Father is greater than I.”
“Thou hast loved righteousness, and hated iniquity; therefore God, even thy God, hath anointed thee with the oil of gladness above thy fellows.”
What the Qur'an says
The Qur'an says every messenger was sent with one message: that there is no god but Allah (﷾), so worship Him alone. Islam teaches that Jesus, like the prophets before him, taught the same. The Qur'an tells the People of the Book (Jews and Christians) not to go to excess in their religion. It says Jesus was a messenger of Allah (﷾), and tells them not to say "Trinity", for Allah (﷾) is one. It warns those who call Allah (﷾) one of three. It sums up who God (﷾) is in four short verses. He is One, He begets not and is not begotten, and there is none like Him.
“Not a messenger did We send before thee without this inspiration sent by Us to him: that there is no god but I; therefore worship and serve Me.”
“O People of the Book! Commit no excesses in your religion: Nor say of Allah aught but the truth. Christ Jesus the son of Mary was (no more than) a messenger of Allah, and His Word, which He bestowed on Mary, and a spirit proceeding from Him: so believe in Allah and His messengers. Say not "Trinity": desist: it will be better for you: for Allah is one Allah: Glory be to Him: (far exalted is He) above having a son. To Him belong all things in the heavens and on earth. And enough is Allah as a Disposer of affairs.”
“They do blaspheme who say: Allah is one of three in a Trinity: for there is no god except One Allah. If they desist not from their word (of blasphemy), verily a grievous penalty will befall the blasphemers among them.”
“Say: He is Allah, the One and Only; Allah, the Eternal, Absolute; He begetteth not, nor is He begotten; And there is none like unto Him.”
Verse by verse
Matthew 28:19 — Gospel of Matthew, chapter 28, verse 19
“Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:”
Cited for
Jesus himself named the Father, the Son and the Holy Ghost together, so the Trinity was taught from the start.
The response
Naming three together is not saying that the three are one God, equal and eternal. In Acts, Peter tells the crowd to be baptised in the name of Jesus Christ. He does not say the name of the Father, the Son and the Holy Ghost.
Where it lands — The verse names three. The teaching that the three are one God was written at Nicaea and Constantinople.
Genesis 1:26 — Torah, Bereshit, chapter 1, verse 26
“And God said, Let us make man in our image, after our likeness: and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing that creepeth upon the earth.”
Cited for
God says "Let us make man in our image", so there is more than one person in God.
The response
The next verse says "God created man in his own image", with a singular verb and a singular "his". One God (﷾) is speaking in the plural of majesty. Kings speak of themselves as "we", and God (﷾) speaks of Himself as "We" throughout the Qur'an. The people who wrote and read Genesis never found a Trinity in it.
Where it lands — One God (﷾) created, as the very next verse says.
Revelation 22:13 — Revelation of John, chapter 22, verse 13
“I am Alpha and Omega, the beginning and the end, the first and the last.”
Cited for
Jesus takes God's own title, the first and the last, so he must be God.
The response
The same book opens by calling itself the Revelation of Jesus Christ "which God gave unto him". In the same book Jesus speaks of "my God" four times in one verse.
Where it lands — Even in Revelation, what Jesus has is given to him by God (﷾).
Philippians 2:6-7 — Epistle to the Philippians, chapter 2, verses 6-7
“who, existing in the form of God, didn’t consider equality with God a thing to be grasped, but emptied himself, taking the form of a servant, being made in the likeness of men.”
Cited for
Philippians says Jesus was in the form of God and equal with God.
The response
Whatever "the form of God" means, the passage goes on to say who holds the higher rank. Jesus emptied himself, "taking the form of a servant". Three verses later Paul says God (﷾) highly exalted him and gave him a name above every name. Paul keeps God (﷾) as the one who gives the rank and Jesus as the one who receives it.
Where it lands — Even here God (﷾) is the one who exalts and Jesus the one exalted.
Perspectives
Mainstream Christian
The Trinity is the faith of the apostles. The councils of Nicaea and Constantinople defended it against error and gave it exact words, but did not invent it.
Matthew 28:19 names the Father, the Son and the Holy Ghost together in one baptism.
Rebuttal
The verse does name three together, but naming three is not saying they are one God, equal and eternal. In Acts, Peter tells the crowd to be baptised in the name of Jesus Christ.
Christians hold that the Creed of Nicaea states in exact words what Scripture already teaches.
Rebuttal
Christians do say so, but the councils fought for decades over the key word. In 357 one council declared the Father greater than the Son. The historian Hanson calls those years a search for a doctrine, not the defence of one already settled. Even a Jesuit historian who believes the doctrine says the New Testament gives no formulated doctrine of the Trinity.
The Islamic perspective
Jesus taught the oneness of God (﷾), as every prophet did. The Trinity was worked out by men over three and a half centuries after him, and made law by emperors. The Qur'an calls it an excess.
The word Trinity is not in the Bible. Even scholars who hold the doctrine grant that the New Testament gives no formulated doctrine of it.
Tertullian admits that most ordinary believers of his day were alarmed by the doctrine.
At Nicaea in 325 the emperor Constantine urged the word homoousios ("of one substance") on the bishops. Arius was exiled by imperial edict.
Decades after Nicaea came the Council of Sirmium in 357. It banned the word substance and declared the Father greater than the Son.
In 380 the emperors ordered all their peoples to believe in the Trinity. In 381 the creed was expanded to say the Holy Spirit is worshipped with the Father and the Son.
The historian R. P. C. Hanson describes the years 318 to 381 as a search for a doctrine of God (﷾) that reached its final form only in 381.
Again and again the New Testament puts God (﷾) above Jesus.
Jesus condemned teaching the commandments of men as doctrines of God (﷾). A doctrine no prophet taught, later fixed by councils and emperors, is such a teaching.
The Qur'an tells Christians not to say "Trinity", because Allah (﷾) is one.