Moab - This is fallen from Psalm 60:8. The only change is in the close of the verse. Instead of “Plilistia, triumph thou because of me” Psalm 60:8, it is here, “Over Philistia will I triumph.” Why the change was made is unknown.
SDA Bible Commentary (limited)
Volume 1-7
9. Moab is my washpot. Moab was notorious for its pride (see Isa. 16:6). Here the psalmist compares this haughty nation to a vessel in which a victorious warrior washes his feet.
Philistia. Early in his reign David had subdued the Philistines (see on 2 Sam. 8:1). God will triumph over all the enemies of His people.