John Calvin Commentary Psalms 125:4

"Do good, O Jehovah, unto those that are good, And to them that are upright in their hearts." — Psalms 125:4 (ASV)

Do good, O Jehovah, to the good. The Prophet has already promised to all the faithful the timely help of God; but still he resorts to prayer, and that for good reason. For although faith may sustain us, yet, as our fleshly sense and reason are wavering, we should add prayers for our strengthening.

Let us then follow this rule of the Prophet. After urging all the faithful to maintain confidence, he also teaches them that instead of remaining passively inactive, they should turn to God, earnestly pleading with him in prayer for what he has instructed them to hope for through his word.

Indeed, the importance of using this remedy is clear when we consider that in the midst of afflictions' darkness, God's help is not perceived. Instead, he may seem to make no distinction between the righteous and the wicked.

The Psalmist does not simply pray that God would deal graciously with the good; he also defines the goodness that characterizes them as proceeding from a sincere heart. It would not be enough for God's children to abstain from all wrongdoing if they were not also distinguished by a corresponding integrity of heart—or rather, if this integrity did not govern their whole life.