The strongest Muslim objection is not the crude slogan "three equals one." It is that core Christian claims about Jesus seem to place created human limits and uncreated divine perfection on the same worshipped person.

How a careful Christian would state the issue

A serious Christian does not usually say, "God is one and three in the same sense." Classical Trinitarian language says God is one in essence and three in persons. Likewise, in the doctrine of incarnation, Jesus is said to be one person with two natures: fully divine and fully human.

So the Christian reply is: there is no formal contradiction unless the same thing is affirmed and denied in the same respect. "One essence, three persons" is not the same as "one person, three persons." "Jesus is mortal in his human nature and immortal in his divine nature" is not meant as "God, as God, died."

That is the strongest form of the argument, and Muslims should represent it fairly. Mocking it as simple arithmetic is not enough.

The specific tension Muslims point to

The deeper problem is about worship, identity, and divine perfection. The Quran teaches that God is utterly one, self-sufficient, unlike creation, and not subject to birth, need, ignorance, suffering, or death:

Say: He is Allah, One. Allah, the Self-Sufficient. He neither begets nor is born, nor is there to Him any equivalent.

Quran 112:1-4

Against that standard, the Christian claim about Jesus raises a real question: if Jesus is worshipped as God, and Jesus also eats, sleeps, grows, prays, suffers, and dies, then the worshipped subject appears to have properties that do not belong to God.

Christians answer by dividing the predicates according to the two natures. Muslims respond that this may avoid an immediate logical contradiction on paper, but it leaves a serious theological difficulty: the believer is still worshipping one personal subject, Jesus, while saying of that same subject things that belong to the Creator and things that belong to creation.

What the Quran rejects

The Quran honors Jesus as the Messiah, born miraculously, a word from God, and a mighty messenger. It rejects making him divine or calling him the son of God in a way that compromises God's oneness:

O People of the Scripture, do not go to extremes in your religion, and do not say about Allah except the truth. The Messiah, Jesus son of Mary, was only a messenger of Allah, and His word which He directed to Mary, and a spirit from Him. So believe in Allah and His messengers, and do not say, "Three."

Quran 4:171

They have certainly disbelieved who say, "Allah is the Messiah, the son of Mary," while the Messiah said, "O Children of Israel, worship Allah, my Lord and your Lord."

Quran 5:72

Notice the Quranic focus: worship. Jesus calls people to worship the Lord; he is not the Lord to be worshipped. That is the heart of the disagreement.

What this does and does not prove

This argument does not prove that Christians are unintelligent, nor does it prove that Christian theology has no sophisticated answers. It also does not work well if stated as "Christians believe 1 = 3," because that is not their best formulation.

What it does establish is that, from the Islamic understanding of God, incarnation and Trinity are not harmless mysteries. They blur the line between Creator and creation, and they give divine devotion to someone the Quran presents as a servant and messenger of God.

So the honest Muslim answer is: the contradiction is not a cartoon of Christian belief. The real difficulty is whether the same Jesus can be truly worshipped as uncreated God while also truly sharing the dependent, limited condition of a human being. Islam answers no, and calls people back to the pure worship of the One God.