Matthew Poole and continuators on Psalms 51:18

18. Do good in thy good pleasure c unto Sion : build thou the walls of Jerusalem .

Synecdochically put for Ierusalem, as the next Clause explains it, and both put for the whole People of Israel and Church of God: whom I have highly scandalized and injured already, and exposed to the Danger of utter Destruction, which thou mightest inflict upon them, for the sins of their King, as thou usest to do in like Cases.

Perfect the Walls and Buildings of that City, and especially let the Temple be built and established in this City, notwithstanding its Pollution by my sins, which I pray thee to Purge away.

Or, For, or according to (for the Hebrew prefix Beth is frequently used, both those ways) thy good Grace, or Favour, or Pleasure, (i. e.) Thy free and rich Mercy, and thy gracious Purpose and Promise, made to and concerning Zion: Of which see Psal. 132. 14. and do not repent of it, nor retract it, as I have given thee cause to do.