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I was saying that another mystery revolves around how did God forgive the sins in the old testament.
Please show me averse in the OT where it explains the basis for God's forgiveness
The Old Testament does explain the basis for God’s forgiveness, and it does so in very clear words. When God revealed Himself to Moses He said, “The Lord, the Lord God, merciful and gracious, longsuffering, and abounding in goodness and truth, keeping mercy for thousands, forgiving iniquity and transgression and sin” (Exodus 34:6–7). This is the foundation: God Himself is merciful and He forgives. He also gave Israel sacrifices as a sign of atonement, saying, “For the life of the flesh is in the blood, and I have given it to you upon the altar to make atonement for your souls” (Leviticus 17:11).
This shows that forgiveness was not earned by men but was given through the blood that God provided, pointing forward to the greater sacrifice of the Messiah.
The prophets also spoke with great clarity. Isaiah declared, “Though your sins are like scarlet, they shall be as white as snow” (Isaiah 1:18), and again, “I, even I, am He who blots out your transgressions for My own sake, and I will not remember your sins” (Isaiah 43:25). Micah marveled, saying, “Who is a God like You, pardoning iniquity and passing over the transgression of the remnant of His heritage? … You will cast all our sins into the depths of the sea” (Micah 7:18–19).
David, too, rejoiced in God’s forgiveness, writing, “Blessed is he whose transgression is forgiven, whose sin is covered” (Psalm 32:1), and again, “As far as the east is from the west, so far has He removed our transgressions from us” (Psalm 103:12).
The basis of this forgiveness was not only mercy and atonement, but also God’s unconditional love. Through Jeremiah God spoke, “Yes, I have loved you with an everlasting love; therefore with lovingkindness I have drawn you” (Jeremiah 31:3). This everlasting love is what moved Him to forgive, to cleanse, and to promise restoration to His people.
All of these verses show that the Old Testament did not leave forgiveness as a mystery. The basis was always the mercy of God, His unconditional love, given through repentance and through the blood of atonement that He Himself provided, which looked ahead to the Messiah. The cross of Christ was the fulfillment of what God had already made known: that He is a God who forgives iniquity, who blots out sins, and who makes the guilty clean. Do you believe this Doug?