The terms Islam and Muslims are revealed names from God, while Christianity and Christians are man-made expressions. Why do Christians accept such names when the Bible never uses them?

In the first place, it really doesn’t matter what the Quran claims about the origin of the words Islam and Muslims since one must first prove that it is a book from the true God. Muslims who assume that these terms are revealed names are really begging the question since they have assumed that the Quran is divine revelation, but have failed to prove their case thus far. Secondly, why is it necessary to show that the name Christian(s) is a divinely revealed name? What makes Muslims think that they can impose their understanding upon the Christian faith and that Christians must meet their criteria? Christianity is not Islam and the two religions are not identical in their understandings of revelation. For instance, the Muslim view of revelation is that the Quran was sent down ('tanzil') directly from heaven, untouched in any way by the messenger, which was then dictated to Muhammad. The biblical understanding of inspiration is different, i.e., God working with and through his people. Furthermore, the Bible teaches that God works out everything according to his sovereign purposes. What this means is that even if the naming of Christ’s followers as Christians wasn’t directly revealed by God, it still didn’t happen apart from God’s purposes or against his intentions. Their being named such could have only happened if God had intended and purposed it beforehand. This leads me to my next point. It is not correct to assume that the word Christian(s) is a man-made title, as opposed to a divinely revealed name, since there is plenty of evidence from the NT itself to prove that such is not the case. For instance, the Lord Jesus anticipates a time in which his followers would carry his name, that kind acts would be shown to those who believe in him on account of their bearing the name of their Lord. Not long after that, we see how God moved people to start identifying Christ’s followers as Christians, which fulfills the words of Christ.