What would the perfect religion look like? I would argue that Christianity is the perfect religion. It is a religion that has evolved into a powerful psychological drug that is very, very hard to give up, making it the most successful religion to date.
Evolution is a biological process that involves change in species. There is no goal in evolution. We humans are not the pinnacle of several billion years of evolution. We may be more cerebral than any previous species (to our knowledge), but that doesn't mean that evolution has strived to produce us and, now that it has, we are biology's crowning achievement. Evolution doesn't work that way. It could care less if we are here. We are just one tiny leaf on the vast tree of evolution. Once humans are exctinct, the process will just carry on much the same. The evolution of religion is quite different. This is a manufactured process (though not conscious on any individual's level) of gradual change in humanity's approach to the supernatural. It is a process that has gradually made religions better and better at recruiting people and keeping them locked into the religious belief. The perfect religion would presumably be one that causes all humans to believe in it, and to never, ever leave it. Christianity might not be quite there yet, but it's done a better job of that than most if not all religions before it.
Fear and reward are important themes in religion. There is much to be afraid of in this world. Primitive hominids had to be afraid of being prey, of lightning, of the dark, of death itself (once they evolved the ability to recognize that inevitability). Reward plays a big role in human psychology. We all seek rewards, whether we consciously recognize it or not. Much of our daily lives are occupied with seeking out ways to enhance complex releases of rewarding neurotransmitters in the brain that make us feel good. Some of these rewards are short-lasting and instant such as those involving a cup of coffee or a piece of ingested chocolate. Others are very long-lasting and complex, such as those involving decisions surrounding marriage, career, and having kids. If you have kids, just think, is anything in life more rewarding than your kids? Having a piece of chocolate might feel better for the 30 seconds you are eating it, but then it is gone. Either you have to just revel in the knowledge that you rewarded yourself with the pleasure of eating it, or you become an addict, constantly seeking out your next chocolate hit. But longer acting rewards such as children and career provide you with a deep sense of well-being and satisfaction. A constant background level of rewarding neurotransmitters that make you feel good about yourself all the time, not just for the fleeting 30 seconds associated with a good piece of food or with a drug.
So, something in life that could calm your natural fears about your surroundings and at the same time provide you with a deep sense of satisfaction and reward would likely be very successful with humans. It would be...addictive.
Now, think about what can do that. What could take away all your fears, including the fear of your impending and unavoidable death, and at the same time give you a long-lasting feeling of reward and satisfaction? Well, religion can do that.
In the good old polytheistic days, humans managed to tackle the fear side of things. Praying to the gods seemed to occasionally convince them not to send a thunderstorm or a flood this time. Sacrificing a virgin to the gods seemed to help out with a good growing season. And, if it didn't, then there was always a way to find something that someone had done wrong that must have angered the gods and over-ridden your costly sacrifice. But, the provision of a sense of control did take care of some of the fear. After all, most of us are most afraid of being out of control. Whatever you are afraid of in life, whether it is heights, snakes, sharks, or rats, you're likely much more afraid of them when you are in a position in which you have no control. How fearful it is to children when a bully comes through the playground and forces them to come face to face with a rat or snake compared to just knowing that a rat or snake is traveling by in the playground. When you can't run away, it gets a lot more frightening. So, the appearance of control over the frightening things in life went a long way to helping humans feel better, and in helping to give religions a firm root in the human psyche. But, it wasn't quite good enough. The reward was lacking.
Along came Christianity (and its spin-off of Islam). Christianity offers an absolute repreive from the most fearful human event: death. And at the same time, it offers the huge reward of knowing that you are going to live in bliss forever. Humans can put up with a lot of misery in the present if they know there is a big reward in the future. Animals don't do this on such long time scales. A dog might perform a trick for the promise of a treat in 30 seconds, but no dog is going to do a trick so that it can get a reward next year. But you might. You might work hard for 40 years of your life just so that you know you'll be rewarded with a solid pension decades in the future. If someone you really trusted was willing to give you a billion dollars ten years from now, you might be willing to put up with almost any misery to get there. Christianity offers the ultimate reward: eternal life in heaven. What wouldn't you be willing to put up with in life to get that reward?
Christianity succeeds where some other religions have failed, in providing that perfect mix of fear and reward. There is just enough fear of death (and a fate even worse than death itself) if you don't accept the religion, mixed with the ultimate reward. It is hard to picture a more fearful punishment than an eternity in hell, and it is hard to picture a better reward than an eternal life in heaven. It is the ultimate combination. That is why I am 100% certain that, despite their denials, almost every Christian would give the religion up immediately if they knew with certainty that there was no punishment or reward after death. Take away those key motivators and the whole thing just crumbles into some vague pre-historic attempt at explaining the supernatural.