Psalm 51 is not a statement of facts as in a courtroom.
The psalmist is acknowledging his position as a sinner before good itself. This Psalm is addressing his infidelity with Bathsheba.
Today we might call David’s sin, infidelity, but in David’s time it was called adultery, on top of that, David arranges to have Bathsheba’s husband killed.
So David says in the psalms,
1 Have mercy on me, O God,
according to your unfailing love;
according to your great compassion
blot out my transgressions.
2 Wash away all my iniquity
and cleanse me from my sin.
3 For I know my transgressions,
and my sin is always before me.
4 Against you, you only, have I sinned.
Supposing that when David and Bathsheba stand before Christ, Bathsheba does not accept David’s repentance, would Christ forgive him and grant him eternal salvation?
It almost seems that we sin more against Christ, because he chose to die for us, so that sins may be forgiven.
God is the sole source of all that is good, and the source of all forgiveness. David is not somehow saying he has not wronged others. The statement “you alone” is not exclusive. Maybe it rather recognizes the unique relationship we have with God and the offense we have commited against that unique relationship.
I personally feel it is so much better to forgive, even if the other person is not repentant, because it seems that Christ is more forgiving than we are. Imagine standing before Christ, and he is willing to forgive my enemy, but I still choose to hold onto anger, at what point should I let go?
Jesus you are the living Son of God. Have mercy on us. Thank you for loving us. Thank you for you.
Amen