John's perspective is significant because it gives the most developed New Testament portrait of Jesus as the pre-existent "Word." The real question is whether that perspective proves Jesus' own original message was divine sonship and incarnation, and that is a much harder claim.
How the argument is usually made
The strongest Christian use of John is not shallow. It says: John's Gospel is not a minor text, but one of the four canonical Gospels. It presents Jesus speaking with unique authority: "Before Abraham was, I am," "I and the Father are one," and Thomas says to him, "My Lord and my God." John also says plainly why he wrote:
"These are written so that you may believe that Jesus is the Christ, the Son of God."
John 20:31
So the argument is: if John is a true apostolic witness, then Islam's view of Jesus as a prophet but not God is not just incomplete; it contradicts a major witness inside the Bible itself.
What John's Gospel clearly shows
A fair Muslim should admit that John matters. It is a powerful theological Gospel, and it has shaped Christian belief more than perhaps any other New Testament book. It also shows that, by the time this text reached its final form, some Christian circles were expressing belief about Jesus in very elevated language.
But that is not the same as proving that Jesus himself taught the Nicene doctrine of God. John is markedly different in style and wording from Matthew, Mark, and Luke. In the earlier Synoptic Gospels, Jesus speaks mostly in parables, prayer, worship of God, repentance, and the kingdom of God. In John, long theological speeches dominate. Many biblical scholars, including Christian ones, recognize that John is highly interpretive, not merely a transcript of public sermons.
That does not make it worthless. It means its genre and purpose must be read honestly. John is a theological testimony written to produce faith in a particular understanding of Jesus.
How the Quran frames the issue
The Quran honors Jesus, his Gospel, his miracles, and his purity. But it also says that later communities disputed about him and exaggerated his rank. The Quran's correction is direct:
"O People of the Scripture, do not commit excess in your religion or 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.' Desist - it is better for you."
Quran 4:171
Notice the balance: Jesus is "His word" and "a spirit from Him," so Islam does not reduce Jesus to an ordinary man. But the verse refuses the move from honor to worship.
The Quran also depicts Jesus himself denying that he called people to worship him:
"I did not say to them except what You commanded me - to worship Allah, my Lord and your Lord."
Quran 5:117
What this does and does not establish
John establishes that high Christology became central within Christianity and that Christians who accept the Bible's canon have strong internal reasons to treat John's Gospel as authoritative. That should be acknowledged plainly.
It does not establish, by itself, that John's wording is the exact speech of Jesus, that John's theology overrides all earlier prophetic monotheism, or that the Quran is false. From an Islamic view, the decisive question is not whether later Christians revered Jesus deeply - they certainly did - but whether God revealed that Jesus is to be worshiped. The Quran answers no.
So John's perspective is significant, but not decisive against Islam. It is a major Christian witness to Christian faith; it is not an independent proof that Jesus departed from the worship of the one God he called "my Lord and your Lord."