God is omniscient – he knows everything. This truth is eloquently expressed by the psalmist: "You know when I sit and when I rise; you perceive my thoughts from afar. You discern my going out and my lying down; you are familiar with all my ways. Before a word is on my tongue you know it completely, O Lord... Where can I go from your Spirit? Where can I flee from your presence? If I go up to the heavens, you are there; if I make my bed in the depths, you are there. If I rise on the wings of the dawn, if I settle on the far side of the sea, even there your hand will guide me, your right hand will hold me fast... All the days ordained for me were written in your book before one of them came to be." (Psalms 139:1-16) The prophet Jeremiah learns of the omniscience of God when he is told, "Before I formed you in the womb I knew you, before you were born I set you apart; I appointed you as a prophet to the nations." (Jeremiah 1:5) Yet an all-knowing God says, "I will remember their sins no more." (Hebrews 8:12; Jeremiah 31:31-34) That statement is at the very heart of the new covenant.
How can it be, then, that an all-knowing God does not remember our sins? Does God erase them from his memory? Does he block them out of his mind? How does this divine amnesia work?
God "not remembering" our sins is set in contrast to the covenant given through Moses, where animal sacrifices were offered "as an annual reminder of sins". (Hebrews 10:3) Those sacrifices continued to be offered, though it was "impossible for the blood of bulls and goats to take away sins". (Hebrews 10:4) These sacrifices could not satisfy the justice of a holy and righteous God; they could never atone for our sins. But they did point to a time when God would provide the perfect sacrifice to take away our sins. Jesus is that sacrifice; he is "the Lamb of God who takes away the sin of the world". (John 1:29) Through his perfect sacrifice, Jesus made atonement for our sins and "where these have been forgiven, there is no longer any sacrifice for sin." (Hebrews 10:18) If we trust in the sacrifice of Jesus, God treats us as if we had never sinned. We are regarded as sinless. No longer does God remember those sins because they no longer exist. That's a holy fact.
The psalmist captured the extent of God's gracious forgiveness in these words: "The Lord is compassionate and gracious, slow to anger, abounding in love. He will not always accuse, nor will he harbour his anger forever; he does not treat us as our sins deserve or repay us according to our iniquities. For as high as the heavens are above the earth, so great is his love for those who fear him; as far as the east is from the west, so far has he removed our transgressions from us." (Psalms 103:8-12) We deserve to be eternally condemned for our sins, but that is not how God treats us. Guilt is pardoned. And to emphasise that pardon the psalmist says, "as far as the east is from the west, so far has he removed our transgressions from us." If he had said, "as far as the east is from the north east..." that would be too close. But east from west is a different picture. The prophet Micah is similarly expressive when talking about God's forgiveness. "Who is a God like you?" he asks, then proceeds to exult the greatness of God "who pardons sins and forgives transgression... you do not stay angry forever but delight to show mercy... you will tread our sin underfoot and hurl all our iniquities into the depths of the sea." (Micah 7:18-19) Notice that our sins are not cast into shallow water, where they could easily be found, but "into the depths of the sea".
God can never forget our sins. How could he? Our pardon from those sins cost him the death of his only begotten Son. How could that ever be forgotten? But because we have been forgiven through Jesus, God now treats us as if we never committed a sin in our life. His gracious treatment of us, his loving acceptance of us is his declaration that our sins are remembered no more.