From Interfaith Dialogue to Apologetics
When the Cantor of Antioch wondered how to explain Christianity to local Muslims, he asked Thomas Aquinas. Thomas answered the cantor with Reasons for the Faith Against Muslim Objections, excerpted below. The translation was provided by Joseph Kenny, O.P., a professor of religious studies at the University of Ibadan, Nigeria.
The following are the things you say the Muslims attack and ridicule: They ridicule the fact that we say Christ is the Son of God, when God has no wife (Qur'ân 6:110; 72:3); and they think we are insane for professing three persons in God, even though we do not mean by this three gods.
They also ridicule our saying that Christ the Son of God was crucified for the salvation of the human race (Qur'ân 4:157-8), for if almighty God could save the human race without the Son's suffering he could also make man so that he could not sin.
They also hold against Christians their claim to eat God on the altar, and that if the body of Christ were even as big as a mountain, by now it should have been eaten up.
On the state of souls after death, you say that the Greeks and Armenians hold the error that souls after death are neither punished nor rewarded until the day of judgment, but are in some waiting room, since they can receive no punishment or reward without the body. To back up their error they quote the Lord in the Gospel (Jn. 14:2): "In my Father's house there are many places to live in."
Concerning merit, which depends on free will, you assert that the Muslims and other nations hold that God's fore-knowledge or decree imposes necessity on human actions; thus they say that man cannot die or even sin unless God decrees this, and that every person has his destiny written on his forehead.
On these questions you ask ...