I came across an early Muslim personality who I found to be very interesting: Ali ibn Rabban Al-Tabari.
A Syriac Christian, son of a Syriac Christian, who served most of his life in the courts of the Abbassids. He had a reputation for his talent as a physician, and he authored the medical work “Firdaws al-Hikmah”. He was close to the caliphs that he served under, sometimes referring to them by their personal names in his works.
It was around the age of 70 when he finally converted to Islam, after which he promptly wrote two treatises against his former faith. Given his command of Syriac and Greek, he was able to engage with the text of the gospels, carefully comparing them to orthodox Christian dogma. Furthermore he seems to express clearly some of his doubts that he had even while he was a Christian: For example, he had serious problems trying to make sense of the doctrine of the incarnation, writing that “These are matters that have driven me away from you Christians.”
His polemical works have recently been translated in the book “The Polemical Works of Ali Al-Tabari,” which I encourage anyone interested in Christian-Muslim dialectic to read.
In his introduction to “al-Radd `Ala al-Nasara”-
On the contrary, in what I have written in this book of mine I have only wanted to come closer to God, great and mighty, and to give a justification and a warning to all Christians. I hope that it will be in the form of advice to them, although I have no doubt that they will avert their heads and ears, turning away and not accepting. But I will gain the reward of a good and well-paid adviser, and those who disapprove of me and condemn me will be committing a blameworthy and grave crime. This does not prevent people of compassion and affection from pursuing truth and offering a justification. A man’s compassion and kindliness for his son may drive him to give him bitter, distasteful, evil smelling medicines to drink, and if a disease affects his body he may even cut off one of his limbs for fear that the disease might speed through his whole body and destroy it. And the destruction of the body, which is a passing affliction, is merely insignificant, but the destruction of the soul is a permanent loss: as Christ (peace be upon him) said to his disciples, ‘Do not fear those who kill the bodies but beware those—cheating and deceiving ones—who kill the souls’.
In what I have set out and established in this book of mine, my intention is not to refute Christ (peace be upon him) or the people of his truth, but those Christian sects that oppose Christ and the Gospels and corrupt the words. No Muslim will peruse this book of mine without increasing joy in Islam, and no Christian will read it without finding himself between two fearsome positions: either to abandon his religion and find fault with its basis, or to find what he believes faulty and to doubt it for the rest of his life, as the proof of reason and correctness of revelation become clear to him, if God almighty wills.
In his polemic concerning the nature of Jesus as both servant and God:
We will ask them about Christ—Is he the eternal Creator as is in their Creed, or is he a chosen man as is in our Creed, or is he God and man as groups of them have said?
If they say, ‘He is a man created and sent’, they agree in their Creed with the Muslims. And if they say, ‘No, he is God, Creator and eternal’, they differ from the Gospels and other books, and they disbelieve in them. For in Chapter 8 in his Gospel, Matthew calls the prophecy of Isaiah to witness that Christ (peace be upon him) was a servant, when he says from God, great and mighty, ‘This is my servant whom I have chosen, and my beloved with whom I am pleased; indeed, I will place my spirit upon him and he will call the nations to the truth’.
This is a clear | statement and not mumbling, and Isaiah was a prophet and not an accuser, and the support for his prophecy is the Gospel. For the servant cannot be divine and the Divinity cannot be a servant, as you have named him.
So, Christians, think about this: The disciple Mark said in his Gospel that when he was on the cross Christ said, ‘My God, my God, why have you forsaken me?’ And this was the last utterance he made on earth. And Matthew says in Chapter 20 of his Gospel that Christ took bread and broke it and gave a piece to the disciples, saying, ‘This is my flesh’. And he gave them a cup containing drink, saying, ‘This is my blood’.
He who has flesh and blood is a body, and every body has length, breadth and depth, and what exists in this manner can be measured and weighed. But God, great is his grandeur, cannot be measured or weighed, because everything that can be measured is bounded and limited, and everything that is bounded decomposes and disintegrates. Luke in Chapter 3 | of his Gospel, describing Christ (peace be upon him) when he was a child, says, ‘The child grew in stature and wisdom and increased before God and people.’ In this Chapter he also says, ‘The child grew and became stronger through the Holy Spirit and was filled with wisdom, and God’s grace was evident upon him.’ It is impossible for the eternal Creator to say that he had a God, or to say that he was a child when the grace of another eternal God was evident upon him.