There are only 2 main reasons why you would follow a religion, like Islam and Christianity, and both have to do with fear.
- The fear of dying, or death, and the possibility of no afterlife.
- And the fear of hell.
With the later, the fear of punishment should be judge unworthy, and suffer eternal torment in hell.
The former, is the quest for eternal life and even the fountain of youth, has been in the mind of men since the beginning of civilisation.
Gilgamesh was a hero, a warrior with a goddess for a mother, so he was demi-god - half god, half man, and there was no other like him, until Enkidu appeared. The 2nd part of the myth of Gilgamesh is about a man's quest for immortality. Since the death of his best friend and blood brother, Enkidu, Gilgamesh felt fear for the 1st time, especially the fear of death. So began his journey that took him to the other side of the world, where he met Utnapishtim.
Utnapishtim was known by his older name, Atrahasis in Old Babylonian, and even older name, Ziusudra in Sumerian. Utnapishtim, or whatever his name may be was the original Flood hero, hence the original Noah, which the Genesis copied and adapted to their Creation Myth. According to all 3 versions on the myth of the flood hero, Utnapishtim or whatever his may be, was given immortality by the gods, hence he is a god.
Gilgamesh asked for immortality, but he failed a test, so no eternal life for him, however Utnapishtim did give him a gift, a food that will restore his youth. But that gift was deprived from him too, because in his journey home, the swallowed the food of youth, while he was distracted.
In older Judaic religion before the Hellenistic influence, there were no such thing as hell being a place of eternal torment. There were no heaven as a place of afterlife. Heaven was place which the god live, and no mortals aspired to live there. All souls went to Sheol. Sheol was not the Christian/Islamic hell, it was not a place of joy or anguish, or of pleasure or pain.
The idea of living in heaven and hell after death was a Greek concept. Christianity have based their concept of afterlife on the late Hellenistic Judaism, as is Islam.
There's no doubt in my mind that Islam copy Christian religion and doctrine, but gave it an Arabic flavour. Muhammad is simply just a model of Abraham, Moses and Jesus rolled into one. There's nothing unique about Muhammad as a prophet, except that he was Arabic one.