When Moses heard that two and a half tribes wanted to stay on the East side of the Jordan, he assumed that they would not go into the Land of Canaan and help the other tribes conquer the land. Therefore, he let them have it, reminding them of forty years earlier when the ten spies discouraged the Israelites,

“So the Lord’s anger was aroused on that day, and He swore an oath, saying, ‘Surely none of the men who came up from Egypt, from twenty years old and above, shall see the land of which I swore to Abraham, Isaac, and Jacob, because they have not wholly followed Me, except Caleb the son of Jephunneh, the Kenizzite, and Joshua the son of Nun, for they have wholly followed the Lord.’ So the Lord’s anger was aroused against Israel, and He made them wander in the wilderness forty years, until all the generation that had done evil in the sight of the Lord was gone. And look! You have risen in your fathers’ place, a brood of sinful men, to increase still more the fierce anger of the Lord against Israel. For if you turn away from following Him, He will once again leave them in the wilderness, and you will destroy all these people” (Numbers 32:10–15).

Moses spoke the truth, but he did not yet know that those tribes would even go into Canaan first, nevertheless, he still spoke a truth that we all need to hear, which is that we do not discourage our brethren through our idleness in the church.