Numbers 32:30

But if they will not pass over with you armed, they shall have possessions among you in the land of Canaan.

Possession in Canaan was made conditional for Gad and Reuben upon crossing the Jordan armed together with their fellow Israelites. The tribes had requested land on their own side, but they were permitted to possess it only if they shared in the fighting ahead. If they refused to go over armed for the common conflict, they were not to keep the land they desired apart. Instead they were to have their possessions among the other tribes inside Canaan itself. The condition shows that seeking one's own temporal advantage does not excuse leaving brethren to bear the common burdens alone.