Religion promises them a new life after death! A kindly world of peace and pleasure with no sickness, woes and unpleasant happenings. Afterlife has been the wish of Rulers throughout history and religious leaders have found a way of controlling the masses, even kings by the use of superstition and the threat of the wrath of gods.
Many, but not all, religions are just a form of mind control. A lot of the times this control begins in children. It is very common in Christianity and is very subtle. It is done by telling people the same things over and over again. It is also done by not giving little children any other information than the religious beliefs.
For somebody to buy in all the way on a religion, they need to think how the religious texts of it think and obey what they say to do. So, in a way, it's an indirect form of mind control. That's likely not the reason for any religions origin (besides Scientology, if you want to count that as a legitimate one for some reason) but that is a result.
Religion is often used to suppress free thinking and crush new ideas and innovation. It can be twisted to create justification for any idea and cast doubt on any counter argument. People who are weak- willed and weak-minded are easily swayed by the charismatic religion mongers and are lead off as new believers without much thought to the contrary.
Religion is not a form of mind control. Although religion is sometimes coercive, it does not actually brainwash people. Religions that brainwash people are called cults, and they are fundamentally different from legitimate religions. In all major religions, the element of free will is important. People must freely choose to believe.
Religious cults could easily be argued as mind control institutions. However, ordinary religions aren't a form of mind control by any means. Regular religions offer people hope and consolation throughout their lives, and we shouldn't penalize people for being a part of a religion. There's nothing wrong with religion today.
Children need religion to help make sense of the world. When religion is taken out of anything, the sense of morality toward human life is stolen. For example, when religion is taken out of school, they are just replacing one religion with another, as atheism is a religion in of itself.