As anyone who knows the Lord can testify, sin separates us from God.
The good news is that the Lord has put in place a system to heal the breach caused by sin and to bring us back to Him. At the center of this system is, of course, the sacrifice.
There are basically three kinds of sin depicted in the Old Testament, each corresponding to the sinner’s level of awareness while he or she committed the transgression: inadvertent or unintentional sin, deliberate or intentional sin, and rebellious sin. The “purification offering” prescribed in Leviticus 4:1–5:13 applied to cases of unintentional sin, as well as some cases of deliberate sin (Lev. 5:1). While an offering was available for these first two categories, none is mentioned for rebellious sin, the most heinous kind. Rebellious sin was done “in the face” of God, with a high hand, and the rebel deserved nothing less than to be cut off (Num. 15:29–31); however, it seems that even in these cases, such as with Manasseh, God offered forgiveness (see 2 Chron. 33:12-13).
Is God justified in forgiving the sinner? After all, is not the sinner unrighteous and, therefore, worthy to be condemned (see Deut. 25:1)?
The story of the woman of Tekoa can illustrate the answer. Pretending to be a widow as instructed by Joab, she went to King David, seeking his judgment. Joab contrived a story about her two sons, one having killed the other, that he asked her to tell David. Israelite law demanded the death of the murderer (Num. 35:31), even though he was the only male left in the family. The woman pleaded with David (who functioned as judge) to let the guilty son go free.
Then, interestingly enough, she declared: “ ‘let the iniquity be on me and on my father’s house, and the king and his throne be guiltless’ ” (2 Sam. 14:9, NKJV). Both the woman and David understood that if the king would decide to let the murderer go free, then the king himself would acquire the guilt of the murderer and that his throne of justice (that is, his reputation as judge) would be in jeopardy. The judge was morally responsible for what he decided. That is why the woman offered to take over this guilt herself.
Similarly, God takes over the guilt of sinners in order to declare them righteous. For us to be forgiven, God Himself must bear our punishment. This is the legal reason why Christ had to die if we were to be saved.