Psalm 109:21

He does not say, "Because my case is good", but because thy mercy is good. Note this also, he does not simply say, Because thou art good, or because thou art merciful; but because thy mercy is good. He had experienced a certain special goodness in the Divine mercy; i.e., such timeliness, kind readiness in all afflictions, and help for every kind of affliction prepared and provided. On this he rests hope and confidence, in this takes refuge. All those are truly happy who have had experience of this mercy, and can depend on it with firm hope and confidence. --Wolfgang Musculus.

Verse 21. Unto a truly broken, humbled sinner, the mercies that are in God, out of which he pardons, should have infinitely more of goodness and sweetness in them than the pardon itself, or all things else that are in the promises. This a soul that hath tasted how good the Lord is will instantly acknowledge. A promise of life to a condemned man is sweet, for life is sweet, as we say; but "thy lovingkindness", said David, who had tasted how good the Lord is, "is better than life", and infinitely sweeter, Psalms 63:3 . And again says David, Because thy mercy is good, deliver thou me. Deliverance was good; yea, but the mercy of God apprehended therewith was infinitely more good to him, which was the greatest inducement to him to seek deliverance. And indeed God's mercy doth eminently bear the style of goodness. --Thomas Goodwin.

Verse 21-25. The thunder and lightning are now as it were followed by a shower of tears of deep sorrowful complaint. --Franz Delitzsch.

HINTS FOR PASTORS AND LAYPERSONS

Verse 21. The plea of a believer must be drawn from his God, his "name" and "mercy." The opposite habit of searching for arguments in self very common and very disappointing.

Verse 21. The peculiar goodness of divine mercy.