Deuteronomy 3:20, commentary and pictures

Moses commands Reuben, Gad, and half Manasseh to leave their wives, little ones, and cattle in their cities east of the Jordan and pass over armed before their brethren to help them conquer and possess the land west of the Jordan, and only when the Lord has given their brethren rest and possession as well is each man to return to his own possession.
The rest promised is settled, quiet, and peaceable possession of the land of Canaan as an inheritance granted by God, including rest from oppression and from all enemies round about so as to dwell in safety.
It was to be received by all only as those already settled helped their brethren obtain it.
That rest was given under Joshua when Israel possessed and dwelt in the land, and it was denied to the rebellious generation whose carcasses fell in the wilderness.
It is not the weekly seventh-day Sabbath, but that land-rest and inheritance is the rest of Hebrews 4 and a figure of the heavenly Canaan and the true rest and inheritance still remaining for God's people.

Context and Command

Deuteronomy 1 to 3 belongs to the three addresses given by Moses just before his death, with the first address in chapters 1 to 4:40 rehearsing God's goodness to Israel. In that setting the command is directed to the two and a half tribes settled east of the Jordan, Reuben, Gad, and half Manasseh. They were to leave their wives, little ones, and cattle in their cities and pass over armed before their brethren to help them conquer and possess the land west of the Jordan. They were to continue that help until the Lord had given rest and possession to their brethren as well, and only then was every man to return to his own possession east of the Jordan which had been given to him. The return was thus made conditional on all having received their inheritance and rest, with the eastern tribes helping their brethren conquer and possess the land west of the Jordan first.

Those who held a different wording of the direction read it as requiring the tribes to help their fellow Israelites obtain rest and possess the land east of the Jordan before returning to their own land. In the same vein, others read it as requiring Israel to wait until the Lord had given the tribes settled east of the Jordan rest and possession of their land before the other Israelites returned to their own inheritances.

Nature of Promised Rest

The rest is being established in the land God had given, quietly and peaceably possessing Canaan as a settled inheritance granted by God after taking possession. Rest and inheritance belong together, for the eastern tribes were to help their brethren take possession west of the Jordan and only then return each man to his own possession east of the Jordan. It is Israel's settled possession of the promised land, granted after the people had taken possession of it. The promise includes rest from oppression and from all enemies round about so as to dwell in safety as much as possession of the land itself. That rest from enemies is the same rest promised in the seed possessing the gate of his enemies, and the same rest of which it is said they had not yet come to the rest and to the inheritance until after crossing the Jordan God would give them rest from all enemies round about. It was Israel's rest from its enemies after taking possession of the promised land under Joshua.

The rest was to be received by all only as the tribes who had received land east of the Jordan helped their brethren conquer and possess the land west of the Jordan, and once all had received inheritance and rest the eastern tribes could return to their own possessions. This rest is peaceful possession of the land, not the weekly Sabbath or the seventh-day Sabbath. It is not the reason the seventh day was made holy. The rest of Hebrews 4 is this possession of the land the Lord gave Israel.

This rest was given by Joshua and fulfilled when Israel possessed and dwelt in the land with rest from enemies round about. It had been sworn away from the rebellious generation so that those whose carcasses fell in the wilderness did not enter it. The armed men of Reuben, Gad, and half Manasseh were to leave wives, little ones, and cattle in their cities and pass over armed before their brethren until the Lord had given rest to their brethren as well, and then each man would return to his own possession. That land-rest and inheritance given under Joshua is a figure or type of the heavenly Canaan and of the true rest and inheritance still remaining for God's people. It was a real, settled inheritance, but it did not exhaust the fuller rest and inheritance still promised.