In my initial response to Mushtaq, I have explained why the whole methodology he is following is fatally flawed. Christ wrote no book, He is the Word, and He founded a Church, and that Church is the body which established both the nature of the NT and of the Trinity: the two go together, and to use to book to disprove the doctrine is pointless, as that is to misread the book.
Nonetheless, let us deal, patiently and with prayerfulness, with the points raised by Mushtaq. His full text can here found on the special page ‘Dialogue with a Muslim’.
Mushtaq asks why none of the prophets nor Jesus used the words ‘Three’ or ‘Trinity’ or ‘Triune’. This is explained in my post here ‘Dialogue with a Muslim’. Jesus established a Church which used these words. It did not, as Mushtaq implies, simply stumble across them in the fourth century. Jesus Himself told His followers to:
Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit,
It is from here, as well as many other NT passages that the Church founded by Jesus Christ, the Son of God, drew its doctrine of the Trinity. See, for example, what the Blessed Apostle John writes:
“By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God… God’s love was revealed among us in this way: God sent his only Son into the world so that we might live through him… By this we know that we abide in him and he in us, because he has given us of his Spirit. / And we have seen and do testify that the Father has sent his Son as the Savior of the world. / God abides in those who confess that Jesus is the Son of God, and they abide in God.”
Here too, there are “Three”. To state that the word ‘Trinity’ is not used, is correct, but to state that the concept of the three, and the Father, Son and the Spirit are not taught in Sacred Scripture is to err. To say that such passages are anything to do with the ‘Royal we’ is to err.
It is to deny the prophetic witness of the Beloved Apostle. John here:
Who is it that conquers the world but the one who believes that Jesus is the Son of God? This is the one who came by water and blood, Jesus Christ, not with the water only but with the water and the blood. And the Spirit is the one that testifies, for the Spirit is the truth.
Who can dare say that the Book canonised by the Church founded by Christ does not bear witness that He is the Son of God, and that the Spirit does not so testify? Who can say that Christ and the Father are not one in the face of the words of St John at the beginning of his magnificent Gospel:
In the beginning was the Word, and the Word was with God, and the Word was God. 2 He was in the beginning with God.
So, no, Mushtaq, you have not shown that the Book canonised by the Church founded by Christ, does not speak of the Father, Son, and Holy Ghost, or that it does not use the figure of three when it describes God; neither have you shown it is anything to do with the Royal Plural. These are but attempts to avoid the Truth taught from the beginning, that Jesus is the Son of God, and that God is Father, Son and Holy Spirit. Jesus Himself told His disciples to baptise in those names.
So, in the face of this, for Mushtaq to quote from Old Testament prophets, who had not been enlightened, is as useless as to quote from the Koran. The prophets of old Israel had not had the full enlightenment given to John and the Apostles; the prophet of Islam had even less enlightenment as he turned away from what had been revealed to mankind through Christ and His Church.