Tawhid
Associating any other thing or person as being comparable to God is called shirk in Islam. This is the only sin in Islam which cannot be forgiven by God, unless a person turns repentant on Earth. The Koran can also be interpreted as telling Muslims to not follow the idea of the "trinity," the Christian concept for explaining God. Since the trinity views God as being made up of three different parts, many Muslims view this as shirk. On the other hand, Christians will say that they view the trinity as making up one God, so it is not shirk. The Koran also says that Jesus did not claim to be anything more than a human being, while in Christianity he is part of the trinity. According to Muslim scripture, Jesus claims to be prophet chosen by God, different from the divine status he has in Christianity.