1 Because there was there a sacrifice after the order of Aaron, and afterwards He of His Own Body and Blood appointed a sacrifice after the order of Melchizedek; He changed then His Countenance in the Priesthood, and sent away the kingdom of the Jews, and came to the Gentiles. What then is, “He affected”? He was full of affection. For what is so full of affection as the Mercy of our Lord Jesus Christ, who, seeing our infirmity, that He might deliver us from everlasting death, underwent temporal death with such great injury and contumely? “And He drummed:” because a drum is not made, except when a skin is extended on wood; and David drummed, to signify that Christ should be crucified. But, “He drummed upon the doors of the city:” what are “the doors of the city,” but our hearts which we had closed against Christ, who by the drum of His Cross has opened the hearts of mortal men? “And was carried in His Own Hands:” how “carried in His Own Hands”? Because when He commended His Own Body and Blood, He took into His Hands that which the faithful know; and in a manner carried Himself, when He said, “This is My Body.” “And He fell down at the doors of the gate;” that is, He humbled Himself. For this it is, to fall down even at the very beginning of our faith. For the door of the gate is the beginning of faith; whence begins the Church, and arrives at last even unto sight: that as it believes those things which it sees not, it may deserve to enjoy them, when it shall have begun to see face to face. So is the title of the Psalm; briefly we have heard it; let us now hear the very words of Him that affects, and drums upon the doors of the city.
2. “I will bless the Lord at all times; His praise shall be ever in my mouth”. So speaks Christ, so also let a Christian speak; for a Christian is in the Body of Christ; and therefore was Christ made Man, that that Christian might be enabled to be an Angel, who says, “I will bless the Lord at all times.” When shall I “bless the Lord”? When He blesses you? When the goods of this world abound? When you have great abundance of grain, oil, and wine, of gold and silver, of servants and cattle; when this mortal health remains unwounded and sound; when all that are born to you grow up, nothing is withdrawn by immature death, happiness wholly reigns in your house, and all things overflow around you; then shall you bless the Lord? No; but “at all times.” Therefore both then, and when according to the time, or according to the scourges of our Lord God, these things are troubled, are taken away, are seldom born to you, and born pass away. For these things come to pass, and thence follows penury, need, labour, pain, and temptation. But you, who hast sung, “I will bless the Lord at all times: His praise shall be ever in my mouth,” both when He gives them, bless; and when He takes them away, bless. For it is He that gives, it is He that takes away: but Himself from him that blesses Him He takes not away.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)