There are two main questions Jews and Muslims ask Christians:
1. How can God be one and three?
2. Why does someone else, never mind Jesus, or God!, need to die so that you can be forgiven of your sin? Surely, repentance should be enough. What’s with, ”the chasening for our well-being, for our true Shalom, fell upon him” (Isaiah 53)? Our iniquity falling upon an innocent, and on the Son of God? Christian, you are shirking your responsibility, says the Muslim, and thus deserve damnation.
What is important is that God’s revelation does not have to fit in with human wisdom, which 1 Corinthians makes clear:
For the word of the cross is folly to those who are perishing, but to us who are being saved it is the power of God. For it is written,
“I will destroy the wisdom of the wise, and the discernment of the discerning I will thwart.”
Where is the one who is wise? Where is the scribe? Where is the debater of this age? Has not God made foolish the wisdom of the world? For since, in the wisdom of God, the world did not know God through wisdom, it pleased God through the folly of what we preach to save those who believe. For Jews demand signs and Greeks seek wisdom, but we preach Christ crucified, a stumbling block to Jews and folly to Gentiles, but to those who are called, both Jews and Greeks, Christ the power of God and the wisdom of God. For the foolishness of God is wiser than men, and the weakness of God is stronger than men.
(1 Corinthians 1:18-25 )
Jews and Muslims believe that the New Testament texts we have today, are at best, corrupt, at worst, a forgery. The frustration for Christians is that the Jew and the Muslim do not apply the same standards of textual analysis (how we arrive at the veracity of the historical record) to their respective texts that they apply to the New Testament. The Jew maintains that he doesn’t need more evidence for his religion than the “fact” that he, together with every other (believing) Jew throughout history, witnessed (vicariously?, mystically?, kabbalistically?) the reality of God at Sinai. And the Moslem?
Well, he just ignores your plea to apply the same rules of texts to his religion. ”Unless you show me an mp3 (Maximum Proof 3nity) of what you say Jesus and Paul said (I think of Bart Ehrman, the Muslim’s guru), I remain, ehr, unconvinced, man”
24 Thomas, one of the twelve, called Didymus, was not with them when Jesus came. 25 The other disciples therefore said unto him, We have seen the Lord. But he said unto them, Except I shall see in his hands the print of the nails, and put my finger into the print of the nails, and thrust my hand into his side, I will not believe.
26 And after eight days again his disciples were within, and Thomas with them: then came Jesus, the doors being shut, and stood in the midst, and said, Peace be unto you. 27 Then saith he to Thomas, Reach hither thy finger, and behold my hands; and reach hither thy hand, and thrust it into my side: and be not faithless, but believing. 28 And Thomas answered and said unto him, My Lord and my God. 29 Jesus saith unto him, Thomas, because thou hast seen me, thou hast believed: blessed are they that have not seen, and yet have believed.