Per the Bible, this story starts around 8,000 years before Jesus came along. The Hebrews, an obscure ethnic group in the Middle East consisting of a handful of purportedly related tribes allegedly descended from twelve sons of one man, had a personal god they believed only spoke to them.
To hear them tell it, their god was holy, righteous, just, and loving, and he created the world we know in a perfect state. He made a man named Adam and a woman named Eve, stuck them in a lovely garden called Eden, gave them his blessing, and left them free to roam as they pleased. Unfortunately, so the story goes, they abused his trust, which led to the loss of that initial blessing and caused humankind to be at odds with the deity. But this god planned to undo many of the effects of this fall from grace.
A little further down the line, they claimed, this plan was set in motion when their god called a man named Abraham to follow him and struck a bargain: “If you follow me, I’ll make you the father of a great nation, and one day your descendants will inherit the land of Canaan.” That sounds like a swell deal, right? With Abraham’s descendants on board, this deal was the start of a new relationship with their god to replace the broken one, a blessing that would cause them to be a blessing to others to reverse the curse, and they’d get a new land to replace Eden. Abraham’s descendants were their god’s chosen people and, to their way of thinking and literature, the only true “children of God.”
Over time, their god built on this plan and added more conditions. Through Moses, the people were given a law (both written and oral), and their god coming through on his promises became conditional on obedience to this law, which they called the Torah. There were 613 rules to follow in the Torah, of which the 10 Commandments are the best known. Among them, there was a particular method of atonement – a means of achieving forgiveness – for sin (the term for man’s disobedience to their god). To receive forgiveness for one’s sins, one had to offer sincere prayers of repentance, turn away from the offense, and offer appropriate sacrifices as recompense. (Later, this would be done at the Temple in Jerusalem.) The prize was the land and life after death.
(It’s not especially apropos of anything, but this particular point will become relevant when Jesus comes along: at that time, women had virtually no rights, were supposed to wear veils in public, were not allowed to interact with men in most situations, could not discuss the events of the day, offer opinions, and were not to be spoken to; women didn’t matter. There was even a well-known saying: “Better that the Torah be burnt than given into the hands of women.” Hebrew men thanked God every day that they were not born a woman. Check the Old Testament book of Leviticus for the ugly truth.)