Psalms 89:22

The enemy shall not exact upon him; nor the son of wickedness afflict him.

The promise guarantees that no enemy will be able to exact tribute or impose oppression upon the appointed ruler of David's line. No son of wickedness will be allowed to afflict or bring him low. This protection was pledged as part of the covenant promises made to David and to his house. Those promises find their complete fulfillment in Christ as the final heir of David.