Religion is primarily ... about US. Our place and purpose in the universe, our lack of control of what happens and our monotonous/depressing reality of our life etc..
We created the construct of god, an abstract idea of a powerful being that in control of everything. A being that find each and one of us special, that listen to our prayers and thoughts, that loves and cares about us despite our many faults and failing and most importantly forgive us! In this fairytale God made us and everything for a reason and with a purpose, and despite the hardship we should go on no matter what, because at the end of the tunnel haven is awaits us..
But Religion is much more than belief in god, its away of life. It provides sense of community, so we feel that we are apart of something, that we belong and a reason for people to get together. It provided a support system(priests), someone to talk too. It provide a reason for people to wakeup in the morning and continue to go on.
On top of that for the time, the bible as a collection of wisdom and stories passed over sentries also provide some good practice and values for life. Though of course today its got little outdated and superseded in the literary sense. It was also used as an excuse for many crimes, but I think we all smart enough to realize that people don't lack for excuses when they need them.
Also a little bit off topic. IMO religion was very influential tool for humanity and with its modern rejection, many people lost "their way". Not in a sense that religion is what we need, but that in the short time that our society had so many changes, that many haven't found an alternative system that offers similar benefits for them, sure
we have other ways for self delusion and escape, but from from my perspective they are not as good in some respects.