A broken and a contrite heart

The sacrifices of God are a broken spirit,
A broken and a contrite heart—
These, O God, You will not despise. (Psalm 51)

David knew also how acceptable true repentance is to God (v. 17): The sacrifices of God are a broken spirit. See here,

(1.) What the good work is that is wrought in every true penitent-a broken spirit, a broken and a contrite heart. It is a work wrought upon the heart; that is it that God looks at, and requires, in all religious exercises, particularly in the exercises of repentance. It is a sharp work wrought there, no less than the breaking of the heart; not in despair (as we say, when a man is undone, His heart is broken), but in necessary humiliation and sorrow for sin. It is a heart breaking with itself, and breaking from its sin; it is a heart pliable to the word of God, and patient under the rod of God, a heart subdued and brought into obedience; it is a heart that is tender, like Josiah's, and trembles at God's word. Oh that there were such a heart in us!

-Matthew Henry