Psalms 51:18

May it please you to prosper Zion,

to build up the walls of Jerusalem.

(v18, NIV)

Zion typically refers to Jerusalem. The second phrase in this verse even refers to Jerusalem. This is God's promised land, promised to Abraham. By asking to prosper Jerusalem, David is asking God to prosper the Israelites. These are God's chosen people and as God's chosen people David hopes that God would want to prosper them. The alternative will be famine and plague and death and destruction. Those things may be punishment as a result of sin. Prosperity often coincided with Israel turning back to God and away from sin. David in seeing the error of his ways is repentant and turning away from his sin. We see his brokenness about the wrong he has done. David hopes for prosperity in tandem with God's delight in his broken and contrite heart.