In an attempt to answer of how to make sense of sin, the first thing is to realise that all religion is fantasy, it is not the product of evidence but of the human imagination.
Sin is like being told you have a specific illness that only one known doctor can cure and his agents are everywhere directing your life and making demands on you to conform to his wishes. Once you believe you have sin, they (the religions) are your masters, you have lost freewill!
"Sin entered into the world through our first parents." This is completely untrue, we were never perfect in the first place, we do not originate from two individuals but from millions of antecedents and ultimately from different species of humans, and there is no such thing as a perfect/imperfect division of life -- except in religion. So the remedy for the Genesis fable is to create another one, through the sacrifice of a 'perfect' man. It takes no deep thinking to be able to understand the attractive myth which is in religious terms, that belief in Jesus means getting rid of sin.
The human creation story is so clearly a fable that any intelligent person can see that it's not worth believing since a large part of humanity lived before the time of the would- be Adam and Eve. Even their names Adam = man and Eve = mother of all, puts the story into the fable category because it is one of the ways of determining what a fable is; if the characters names have literal meanings relevant to the story....and not forgetting talking snakes.
Sin must rank as the least helpful concept in developing sound reasoning and a mature response to life's problems.