Albert Barnes 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 Lord, unto those that be good ... — To the good; to the pious. Let them be under the divine protection. Possibly this is not merely a prayer, but is expressive of the belief of the psalmist as to what would occur under the divine administration—that the favor of God would rest upon his people.