The main commonalities are that they both originated in the Middle East and also have common holy lands. They are both monotheistic religions, believing in just one personified God, and are religions that have just one supreme book of revelations in which their followers have recorded their absolute teachings (the Bible and the Qur’an). Further, Islam takes the position that God in the Bible and Allah are the same and also includes part of the Bible in its sacred book (Christianity does not acknowledge that its God is the same as Islam’s God).
In the world of myths and literature, the prototype of human relations, by which people compete as rivals, is that of “brothers”. As can be seen in the table on the left, both Christianity and Islam originally arose from Judaism, have much in common, and are very similar to each other. They look just like brothers, which is why they may compete and clash from time to time.
Editor’s note: Some of the differences and commonalities are not explained properly (especially regarding Islam) and hence seems wrong.