Albert Barnes Commentary Psalms 36:10

"Oh continue thy lovingkindness unto them that know thee, And thy righteousness to the upright in heart." — Psalms 36:10 (ASV)

O continue - Margin, as in Hebrew: “draw out at length.” The Hebrew word means “to draw;” hence, “to draw out,” in the sense of “continuing” or “prolonging.” Compare (Psalms 85:5); (Psalms 109:12); (Jeremiah 31:3). The desire of the psalmist here is that God would make the manifestation of his loving-kindness “continuous” or “perpetual” to His people; that it might not be fitful and interrupted, but always enduring, or constant. It is the utterance of a prayer that his favor might always be manifested to his friends.

Your loving-kindness - Your mercy, (Psalms 36:5), (Psalms 36:7). To those who know You. They are Your friends. The word “know” is often used to denote true religion: (John 17:3); (Philippians 3:10); (Ephesians 3:19); (2 Timothy 1:12).

And Your righteousness - Your favor; Your protection. That is, show to them the righteousness, or the glory of Your character. Deal with them according to those just principles which belong to Your character. Compare the notes at (1 John 1:9).

To the upright in heart - Those who are pure and holy in their intentions or their purposes. Compare (Psalms 7:10). All true uprightness has its seat in the heart, and the psalmist prays that God would show his continued favor to those whom he sees to be true in heart to himself.