Moab is my washpot - Moab was a region of country on the east of the Dead Sea, extending as far north as the river Arnon. See the notes at Isaiah 15:1-9. The words rendered wash-pot mean properly a pot or basin for washing, a wash-basin; and the expression is used here as one of contempt, as if he would use it as the meanest vessel is used. It implies that Moab was already subdued, and that the author of the psalm could make any use of it he pleased. It also implies that Moab was not regarded as adding much to his strength, or to the value of his dominions; but that, compared with other portions of his kingdom, it was of as little value as a wash-basin compared with the more valuable vessels in a house.
Over Edom will I cast out my shoe - Edom or Idumea was the country which still remained unsubdued. This David was anxious to possess, though the conquest had been delayed and prevented by the adverse circumstances to which allusion has already been made in the notes at the psalm. On the situation of Idumea, see the notes at Isaiah 34. It was a region whose possession was necessary to complete the acquisition of territory that properly pertained to the promised land; and David was now intent on acquiring it. He here expresses the utmost confidence that he would succeed in this, notwithstanding the adverse events which had occurred. It is supposed that there is allusion in the expression “I will cast out my shoe,” to the custom, when transferring a possession, of throwing down a shoe on the ground as a symbol of occupancy. Compare Ruth 4:7. In the middle ages this was expressed by throwing down a glove; in the time of Columbus, by solemnly taking possession and setting up a cross; in other times, by erecting a standard, or by building a fort. Compare Rosenmuller, Das alte und neue Morgenland, No. 483. The idea is, that he would take possession of it, or would make it his own.
Philistia, triumph thou because of me - On the situation of Philistia, see the notes at Isaiah 11:14. In the margin this is, “triumph thou over me, by an irony.” It may be regarded as irony, or as a taunt, meaning that Philistia was no longer now in a situation to triumph over him; or it may be understood as referring to the exultation and shouting which would ensue on the reception of its sovereign. The former seems to be the most probable interpretation, as the language is undoubtedly intended to denote absolute subjection, and not the voluntary reception of a king. The language in the entire passage is that of triumph over foes.