For God will save Zion - See the notes at Psalms 51:18. That is, he will save his people; he will protect and defend them. This expresses the confident assurance of the psalmist that, whatever might be the existing troubles, God would not forsake his people, but would interpose in their behalf.
And will build the cities of Judah - Though they may now lie waste, or be desolate. See the notes at Psalms 51:18. The general idea here is, that God would be favorable to his land; that he would give success and prosperity to his people; that he would manifest his mercy to them. There is no necessity from the language used here to suppose, as DeWette and Rosenmuller do, that there is an allusion to the time of the exile, and to the restoration of the Jews from Babylon, and that consequently either the whole psalm must have been composed at that time - or (as Rosenmuller supposes) that the last verses of the psalm were added by a later hand, and that thus the whole psalm was adapted to the time of the exile. From Psalms 69:9 it would seem that, when the psalm was composed, the place of public worship was still standing, and the language here, as in Psalms 51:18, is so general that it might have been employed at any time.
That they may dwell there ... - That his people may dwell there according to the ancient promise. The idea is, that he would be the protector of his people, and that all his promises to them would be fulfilled.