Yes, this is such a big subject and incorporates myth and metaphor, psychology and the overreach to make special belief systems that don't need to be special in this way.
As I've mentioned before, hell for the Inuit is a freezing cold place and heaven is rather warm.
And yes, it's not that easy to discover the history and birth of Islam with any real certainty, but it is much less opaque than Christ and Christianity. In the Bible the writings further in time from the living Christ tend to embellish Him more. They introduce a virgin birth and a great range of miracles, He becomes increasingly supernatural.
So yes the nonessential ingredients of religion tend to outweigh the core teachings over time.
As for the bit of Revelation pointed out by Mr Gordon.
It is interesting that -
The woman has the sun at her head and the moon at her feet. Persia and Islam.
She is from God and about to give birth. Law of God and a new religion.
Red dragon, seven crowns and ten heads. Seven dominions of the Ottoman empire and ten rulers names and red for the war and bloodshed.
The dragon would destroy a third of the stars in heaven - a third of Muhammad's immediate family were murdered.
The woman fled into the wilderness and it was said that they should feed her there a thousand two hundred and threescore days, which is 1,260 years. Daniel expresses it as three times and a half, which is also forty-two months, which are twelve hundred and sixty days, which is 1,260 years. In another passage of John's Revelation He speaks of twelve hundred and sixty days.
The year 1260 of the Hejira of Muhammad corresponds to 1844, and there is only one religion that I know of that is founded in Persian, began in 1844 and the founder is claimed to be a descendant of both Daniel and Muhammad.
Consequently the major religions of America all grew from a belief that Christ would return in 1844. Mormons, JW and Seventh Day and the various Millerite movements all have their roots in this year. The year 1844 was called, The Great Expectation, then it became, The Great Disappointment.
