Here's the truth: Your head is up your ass, you really are a hairless ape, your entire species' - entire planet's - existence is purely by chance, and that your life truly has no meaning, other than what you give it.
The reason people believe in these bullshit religions is because when faced with these truths, they just cannot accept it, and need an alternative "reality" to believe in, because, at the very least, the idea that they are alive for no good and real reason whatsoever makes no sense to them.
Christians, Muslims, both have many similarities. One, they believe in writings that, in the case of Christians, a number of ball-tripping dopeheads, or in the case of Islam, one ball-tripping dopehead, came up with after doing too many hallucinogens and believing that they are hearing "God" or some messenger thereof (say, the angel Gabriel, in the case of Muhammed and Islam, or the Metatron, in the case of Christianity.) They tinkered with these hallucinations until they figured out how to brainwash and control people. Mainly because people wanted a meaning of life, and Christianity and Islam both provide that there is one, 'cept we don't get to know it unless we play by their rules, and still then we must play by those rules 'til we die, and then once we're dead, the big man upstairs will finally spill the beans. Unless, of course, you don't play by the rules, then you get to enjoy an eternity of torture. Supposedly.
Oh, I could go on for hours about this. So glad I am an Atheist.