The idea of religious sin is based on the abuse of making people feel guilty. It is like the mentality that makes you feel guilty all the time is a fertile ground for welcoming religious doctrines. You are mistaken, and the only way to not feel bad because of your mistakes or sins is to be forgiven by the god who has total authority of you and all living beings. By offering them a way to not feel bad because of mistakes, and by also encouraging them to feel bad because of mistakes, religion has made people throughout history strongly and addictively attached to religion. Religion feeds upon you feeling guilty. And encourages you to feel guilty. Then offers you the only way to abolish that sense of guilt, which is God’s forgiveness, which makes you feel like you were just born today, good as new, pure and clean. How does it encourage guilt feelings? It tells you that you are supposed to feel guilty because of disobeying God’s commands. And not just that, it also tells you that the only way to get rid of that same guilt it was responsible for cultivating, encouraging, and nourishing is to ask and beg God for forgiveness. Repent you sinner. This is a recipie for making your mind torn apart, dissipating any chance to attempt addressing any issue through rational, reasonable, or logical ways. The same occurs through religious insistence on the idea that if you do not obey God’s commands and believe in the whole religion and follow it in its entirety you will be sentenced to an eternity of suffering, pain, and torture in Hell, but if you do, you will be granted an eternity in heaven where all your dreams will come true, and whatever that you wish to get will be given to you right away, and you will remain in such happiness for good. This makes you torn apart mentally, leading to the same consequences described earlier, simply put, the inability to exercise reasonableness in anything that you face or deal with.
It is well established in psychology and psychiatry that excessive guilt feelings are symptoms of Major Depressive Disorder. It appears that religion pushes you toward suffering from this disorder until you easily lose any resistance to its doctrines, ideas, commands, and teachings. You become a slave to God. Religion wants you to be excessively guilty all the time, and by association, Religion wants you to be depressed all the time, then you will absorb all the religious indoctrination easily without any resistance.
It is good to understand on the mechanisms by which religion gets to people by abusing, in order to understand how can we counter these twisted methods of mass indoctrinations.
Religion is not the only source of bad ideas and bad stuff that happens in this world, but it certainly destroys your capacity to not produce or accept countless bad ideas and beliefs of your own or of other people.