O continue thy loving-kindness unto them that know thee. Here begins the third strophe. Having finished his" instruction," the psalmist passes on to prayer; and is content to ask that God will be in the future such as he has been in the past—that he will "lengthen out," prolong, or "continue his loving-kindness" to his faithful servants, dealing with them as he has hitherto dealt with them (Psalms 36:5, Psalms 36:7), mercifully, graciously, and lovingly.
His faithful servants are "those that know him," because, as Hengstenberg observes, "the true and essential knowledge of God is to be found only in a sanctified mind." And thy righteousness to the upright in heart.
Continue, i.e; to deal justly with those whose heart is right with thee—who, in spite of occasional lapses, are really in heart sincere.