Albert Barnes Commentary Micah 7:19

"He will again have compassion upon us; he will tread our iniquities under foot; and thou wilt cast all their sins into the depths of the sea." — Micah 7:19 (ASV)

He will turn again — who seemed to be turned away from us when we were turned away from Him. He will subdue, or trample under foot (Joel 2:14), our worst enemy, “our iniquities,” as He says, He shall bruise Satan under your feet shortly (Romans 16:20).

Until now, sinful passions had not only rebelled but had also gained mastery over us. Sin subdued us; it was our lord, a fierce tyrant over us; we could not subdue it. Holy Scripture says emphatically of humanity under the law, that we were sold under sin (Romans 7:14), a slave under a hard master, oppressed, weighed down, and unable to throw off the bondage. We have before proved both Jews and Gentiles, that they are all under sin (Romans 3:9); the Scripture has concluded all under sin (Galatians 3:22).

Under the Gospel, God, he says, would subdue sin “under us,” and make it, as it were, our “footstool.” It is a Gospel before the Gospel. God would pardon; and He, not we, would subdue sin to us. He would bestow, “of sin the double cure, Save us from its guilt and power.” Not I, but the grace of God, which was with me (1 Corinthians 15:10).

And You will cast — not some (for “it is impious to look for a half-pardon from God”), but — all their sins into the depths of the sea. So, just as in the passage of the Red Sea not one Egyptian was left of those who pursued His people, so also there will not be one sin that, through Baptism and on Repentance, will not be pardoned through His free mercy.

Just as those who sank as lead in the mighty waters (Exodus 15:10) never rose again, so also our sins, unless revived by us, shall not rise against us for condemnation, but shall in the Day of Judgment be sunk in the abyss of hell, as if they had never been.