Let those now who reverently and worshipfully fear the Lord say that His mercy and loving-kindness endure forever. Psalms 118:4 (AMPC)
The Mercy of the Lord means He doesn’t deal, treat, or relate with us according to our weaknesses, failures, mistakes, wrongs, or sins. Psalms 103:10 (NKJV) He has not dealt with us according to our sins. Nor punished us according to our iniquities.
The Mercy of the Lord is His forgiveness and forgetting of all our sins.
The Mercy of the Lord is His removing our sins from us. It is Him washing, cleansing, and freeing us from all sin.
Psalms 103:11-12 (NKJV) For as the heavens are high above the earth, [So] great is His mercy toward those who fear Him; As far as the east is from the west, [So] far has He removed our transgressions from us.
According to Hebrews 8:8-13 God has made a New and Everlasting Covenant with us which is founded and established on His Mercy. Hebrews 8:12 (NKJV) For I will be merciful to their unrighteousness, and their sins and their lawless deeds I will remember no more.”
Forever and ever God will always deal with us not according to what we’ve done but according to what He has done for us and in us through His Son Jesus Christ. He will always relate with us and treat us based on the Redemption in the Blood of Jesus in which He has forgiven, removed, and remembers no more all our sins.
This is the Mercy of God that never fails.