Imagine a world without evil...without an example for those to NOT follow.
Imagine everybody all happy and singing Smurfette's "La-La" song...people would be offing themselves due to bordem. Evil is needed in this world, the wicked have to be played off the righteous, and vice versa. Just as a world could not exist with pure evil...man would not be able to create it's civilization, everybody would have killed each other off. Hardship, evil deeds and the fight against them fuel man to be better. So, in a sense, The Devil serves a purpose, and is serving God, a way of stoking the flames of man's survival, an quality control system...
It's called the animal kingdom. No rules, only the survival of the fittest, strongest. You either adapt at all costs, imitate other people strategies of survival to insure your own survival or the survival of your offspring.
Schopenhauer, Kant, buddhists....all came to the same conclusion ; life is an infinite circle with no other purpose but to perpetuate itself. Nothing is ever new, everything is always a repetition of something from the past, but we re never aware that we are repeating patterns. Hapiness leads to suffering that leads to hapiness, that leads to suffering, over and over and over again. They all come to the conclusion you have to be good and compasionate while on earth but you should not reproduce because it would mean that you would participate in the perpetuation of suffering which is the ultimate mistake.
Buddhism is essentially nihilistic, and all these views of existence all share the same concept that women are the matrix, the origin of evil, who always want babies and always lure men into giving em babies. They "want" love, yet give birth to more suffering.
When you give birth you also give death and suffering.
Something you can find in christianism with eve eating the apple.
It is always the same story, with some particularities depending of how it evolved in different places of the world. All religions originate in the same behaviors and beliefs our ancestors, homo erectus, developped while struggling to survive. This is how the recent brain (prefrontal lobes) evolved. It's an extension of the old brain (lymbic system and reptilian brain) that has for sole purpose to make us even more tougher and such able to survive.
Surviving = hapiness.
Dying or having low chances of survival compared to others = depression and death.
The funny is that both happy people -good looking, rich, educated- and depressed ones -ugly, uneducated, violent- reproduce.
To believe, to hope for something in the future, is a construction of your brain which makes you want so survive. If you have no hope and dont believe in anything youre existence becomes pointless and you start harming yourself or others. People who have been abandonned, hated, by their family, parents, are more prone to become depressive. They have a low level of serotonin in the brain. People who have been loved by their family have a higher level of serotonine in their brain.