It is written in the Gospel, Injeel according to John that Jesus (a.s.) said to his disciples the following:
12“I have still much to say to you, but it is beyond your reach as yet. 13It will be for him, the truth-giving Spirit, when he comes, to guide you into all truth. He will not utter a message of his own; he will utter the message that has been Given to him; and he will make plain to you what is still to come. 14And he will bring honour to me, because it is from me that he will derive what he makes plain to you.
The ‘Spirit of Truth’ is the Prophet Muhammad (s.a.w.). In fact, one of his titles was ‘The Prophet of Truth’. He was known also as ‘al-Amin’, ‘The Trustworthy One’ before he was proclaimed a prophet. The ‘Truth’ is the submission to one God, the One God of Abraham (a.s.) and Ishmael (a.s.), their forefather. Islam is known as ad-Din al-Haqq, the Religion of Truth. Indeed, with the coming of Islam, Revelation was completed. He did not speak of himself but only what was Revealed; that Revelation being the Qur’an. And he did prophesise many things including tall buildings, aircraft, the End of Days and the coming of the Messiah (a.s.). Some have come to pass. Some have yet to occur. Did he not receive from God of God and reveal it to the world?
Waraqah ibn Nawfal (r.a.) was a Christian and a man of letters. And he knew these Scriptures. And that is why he waited for the coming of the one who would Glorify God. And his name is Muhammad (s.a.w.) – from the Arabic word ‘hamd‘, which means ‘praise’. And is it not true that Muhammad (s.a.w.) did constantly praise God and by his actions glorify Him? The honour that was given the Jesus (a.s.) is the calling back to the Oneness of God and the affirmation of the true teachings of Jesus (a.s.). Jesus (a.s.) and his mother Mary (a.s.) are mentioned in the Qur’an. That itself is a tremendous honour.
That prophesy has come to pass. Islam is not a new faith but a return to what was. It is the belief in One God, and of His Prophets, of the religion of Noah (a.s.), and Abraham (a.s.), and Isaac (a.s.), and Ishmael (a.s.), and Moses (a.s.), and Jacob (a.s.) and Joseph (a.s.), and Mary (a.s.) and Jesus (a.s.).
26“Well, when the truth-giving Spirit, who proceeds from the Father, has come to befriend you, he whom I will send to you from the Father’s side, he will bear witness of what I was…”
And this is what the Qur’an says:
O people of the Book! Commit no excesses in your religion: nor say of Allah aught but 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: (for Exalted is He) above having a son. To Him Belongs all things in the heavens and on earth. And enough is Allah as a Disposer of affairs. Christ disdaineth not to serve and worship Allah, nor do the angels, those nearest (to Allah): those who disdain His worship and are arrogant ― He will Gather them all together unto Himself to (answer). (Surah an-Nisa’:171-172)
The Trinity itself is an innovation that does not appear anywhere in the four Gospels. The closest that one can find it is this:
19“…you, therefore, must go out, making disciples of all nations, and baptizing them in the name of the Father, and of the Son, and of the Holy Ghost…”
In any case, this verse is of dubious origin and not in line with the teachings of Jesus (a.s.) as espoused by much of his surviving teachings in the rest of the Gospels.
7“And yet I can say truly that it is better for you I should go away; he who is to befriend you will not come to you unless I do go, but if only I make my way there, I will send him to you.”
This verse clearly indicates that there is someone to come after Jesus (a.s.). This is the Prophet Muhammad (s.a.w.) himself.