Charles Ellicott Commentary Numbers 24:18

"And Edom shall be a possession, Seir also shall be a possession, [who were] his enemies; While Israel doeth valiantly." — Numbers 24:18 (ASV)

And Edom shall be a possession, Seir also ... — Better, And Edom shall be a possession, and Seir shall be a possession, for his enemies (i.e., the enemies of Israel, or, rather, of the Ruler who was to rise out of Israel). The Hebrew word (oyebaiv), which is rendered “his enemies,” appears to stand in apposition to Edom and Seir, as the word zaraiv (his enemies, or adversaries) in Numbers 24:8 does to “the nations.” Edom was the name of the people, and Seir the name of the country . The prophecy received its primary accomplishment in the time of David (2 Samuel 8:14), but the ultimate accomplishment is to be found in the person and work of Christ (Isaiah 63:1–4).

And Israel shall do valiantly.— Or, shall acquire power or wealth. (Ruth 4:11).