He shall abide before God for ever - Literally, "He shall sit for ever before the faces of God." He shall ever appear in the presence of God for us. And he ever sits at the right hand of the Majesty on high; for he undertook this office after having, by his sacrificial offering, made atonement for our sins.
Prepare mercy and truth, which may preserve him - As Mediator, his attendants will ever be mercy and truth. He will dispense the mercy of God, and thus fulfill the truth of the various promises and predictions which had preceded his incarnation. There is an obscurity in this clause, ינצרהו מן ואמת חסד chesed veemeth man yintseruhu, owing to the particle מן man, which some translate who or what; and others, number thou, from מנה manah, to count. Houbigant, and he is followed by Bishop Lowth, would read מיהוה miyehovah, Mercy and truth from Jehovah shall preserve him. The AngloSaxon has, Mildheartedness, and soothfastness his, who seeketh? which is nearly the rendering of the old Psalter: Mercy and sothfastnes of him, wha sall seke? Dr. Kennicott says, מן man is a Syriasm; and should be translated quaesoutinam, I beseech thee, - I wish, - O that! On this very ground Coverdale appears to have translated, O let thy lovynge mercy and faithfulnes preserve him! The sense I have given above I conceive to be the true one.
He shall abide before God for ever - That is, perpetually; without danger of change, or of being driven into exile. This may allude, however, to the hope which David had that he would always live with God in a higher world - a world where there would be no danger of change or banishment. His restoration to his home, to his throne, and to the privileges of the sanctuary, he may have regarded as an emblem of his ultimate reception into a peaceful heaven, and his mind may have glanced rapidly from the one to the other. On earth, after his restoration, he would have no fear that he would be banished again; in heaven, of which such a restoration might be regarded as an emblem, there could be no change, no exile.
O prepare mercy and truth - literally, divide, or divide out; then, allot or appoint; and then, make ready or prepare. The prayer is, that God would measure out to him, or impart to him, such favor that this desire of his heart would be realized. On the phrase mercy and truth, see Psalm 25:10, note; Psalm 57:3, note; Psalm 57:10, note.
Which may preserve him - They will preserve him. That is, the manifestation of such mercy and truth would make his permanent occupancy of his throne on earth, and his ultimate reception into heaven, secure.