Moab is my washpot; over Edom will I cast out my shoe: Philistia, triumph thou because of me. Moab is my washpot - The Moabites shall be reduced to the meanest slavery.
Over Edom will I cast out my shoe - I will make a complete conquest of Idumea, and subject the Edomites to the meanest offices, as well as the Moabites.
Philistia, triumph thou because of me - John Hyrcanus subdued the Idumeans, and caused them to receive circumcision, and profess the Jewish religion. The words here seem to predict their entire subjugation.
In an essay for a new translation of the Bible, there is what appears to me a correct paraphrase of the seventh and eighth verses: "Gilead and Manasseh have submitted unto me; Ephraim furnishes me with valiant men, and Judah with men of prudence and wisdom. I will reduce the Moabites to servitude; I will triumph over the Edomites, and make them my slaves; and the Philistines shall add to my triumph."