Psa 6:4 Return, LORD, rescue my soul; Save me because of Your mercy.
Looking at the language David uses here, “God comes back to me”, implying that God has turned His back on David due to David’s sin. This actually happened with Israel when they were invaded by Babylon, God allowed them to be conquered because of their sin. Some times we too have found ourselves being punished by God for our sins, so this is definitely something that we can find common ground with.
Nonetheless, David begs God to come back to Him and the pleas for God to have mercy on Him, and points out God’s merciful attribute.
If we fast forward from the Old Testament to the New Testament, God has shows us mercy by sending His Son Jesus into world to pay for our sins against Him. Jesus takes those sins away.
That is something that surpasses all human understanding and just shows how much greater God is than man. On what planet would any parent have their own child executed to pay for the crimes that someone else committed against them? But as David tells us, “because of God’s mercy.”
God is a merciful God, He knows we are going to fall way short of His standard, but God also can’t lie and go against His Righteous laws and just give us a pass either. So through His mercy, we are in essence “not guilty” when we put our trust in His Son.