That last post was depressing! We are all sinners and that sin keep us separated from God. The truly depressing part is there is nothing we can do about it. Not a thing! Left of our own, we are destined to leave this physical life and spend eternity separated from God with no hope or chance to ever get back in His good graces. We will spend eternity with all others who, like us, were sinners in their physical life and never bridged that gap existing between themselves and God.
But there is good news! God does not want us to be separated from Him. In fact He wants us to be a son or daughter in His family. It is reasonable to ask if God wants us so bad why doesn't he just say we are forgiven of all these sins? If He spoke the universe into being and if He loves us so much, why can't he just speak us into his family? Better yet, why does He even want us to be separated from Him in the first place?
It all goes back to the nature of sin. Sin separates us from God and we are the ones who sin. If it were up to God, we would enjoy His presence in our lives and us in His life. That's what He envisioned in the beginning with the creation of Adam and Eve. But, and this is critical, Adam and Eve chose to separate themselves from God by disobeying His commandment. Read the account of that first disobedience in Genesis. Notice in your reading, God did not forgive them. He punished them. This is a basic principle, sin must be punished. That punishment for us is separation from God.
Fortunately, God put a plan into place to bridge that gap caused by our sin. That gap can be closed by a blood sacrifice. The first blood sacrifices were those made by the Jews in the desert after their deliverance from Egypt. The Jewish exiles were instructed to offer a blood sacrifice annually for the forgiveness of their sins. That sacrifice was a perfect animal; perfect bodily and innocent. That practice continued for through the entrance to the promised land, through the time of the prophets, through David's time and though the conquest of the Jews by the Babylonians. When the Jews were allowed to return to their ancestral homes, they rebuild the temple and re-instituted the practice of a blood sacrifice annually for the forgiveness of sins. At the time of Jesus, an annual blood sacrifice was still required.