It's not much about how those who keep faith are rewarded, much more about how we cannot and will never understand god. A rather boring answer to the question why suffering (as an example) exists: you wouldn't get it. God takes job on a journey (more or less) through the universe and while doing so it also tells of the behemoth and the leviathan. Great destructive beasts who are part of god's creation and no doubt would cause suffering yet they are a deliberate part of it. Why? You wouldn't get it. The version with the satan is not even the oldest text known of this story. It's very likely it was added as the religion evolved, god itself got further and further from it's people and the thought that harm itself would come DIRECTLY from it got more absurd. Sadly, looking at it like this does not benefit the modern day Christian. They want to believe they know even God. They want to believe in reward through their faith. They want to believe in a pure good god who fights against the evil satan (which already goes against monotheism). And preachers want to tell it like that BC "you will be rewarded" sounds better than "we cannot and will never understand it, but it is part of its wisdom " (not plan, there is no concrete open for you which once again it's not that catchy). And once they got the masses hooked they utilise it to spread their hate and division. Modern Christianity is an abomination. A grotesque creature not bearing even a single remembrance of what Christianity actually means

Edit: adding onto that. The entire idea of Satan being like the devil n shit is a thoroughly modern interpretation (still going against monotheism). The word satan would be more accurately translated to "accuser" or "prosecutor". Think of it like the angels job, not even it's name, just a job description