Psalms 51:18-19 - Exposition

That this is an addition made to the original psalm, during the time of the Babylonian exile, or later, for liturgical purposes, has been maintained by a large number of the commentators who ascribe the rest of the psalm to David. The chief ground for the supposition is the prayer in Psalms 51:18 , "Build thou the walls of Jerusalem," which has been supposed to imply that the walls were in ruins, whereas under David they should have been, it is thought, in good condition. But it has been pointed out, very justly, that the fortifications of Jerusalem were not complete in David's time, and that both he and Solomon added considerably to them ( 2 Samuel 5:9 ; 1 Kings 3:1 ; 1 Kings 9:15 , 1 Kings 9:19 ). David may well have thought that, as a punishment for his sin, God might interfere with the work which he was doing for the benefit of his people, and hence have felt it needful to pray, "Do good unto Zion: build thou the wails of Jerusalem."