Deuteronomy 33:21

The first part; the first-fruits of the Land of Promise, the country of Sihon, which was first conquered, which he is said to provide for himself, because he desired and so obtained it of Moses, Num 32. A portion of the lawgiver, i.e. of Moses, whose portion this is called, either because this part of the land beyond Jordan was the only part of the land which Moses was permitted to enter upon; or because it was given to him by Moses; whereas the portions beyond Jordan were given to the several tribes by Joshua, according to the direction of the lot. Was he seated, Heb. hid or protected; for their wives and children were secured in their cities, whilst many of their men went over to the war in Canaan. He came with the heads of the people, i.e. he went, or he will go, (the preter tense being put for the future, after the manner of the prophets,) to wit, to the war in Canaan, with the princes, or captains, or rulers of the people of Israel, i.e. under their command and conduct, as indeed they did; or with the first of the people; or, in the front of the people, as the Syriac renders it; for this tribe and their brethren, whose lot fell beyond Jordan, were to march, and did march, into Canaan before their brethren, as it is expressed, Joshua 1:14. And the Hebrew word rosch oft signifies the beginning or first of a thing. He executed the justice of the Lord, and his judgments with Israel, i.e. he did or will execute the just judgment of God against the Canaanites, as the rest of the Israelites did; he will join in the war against them, as he promised to do, Numbers 32:27, and actually did, Joshua 1:14.