Numbers 26:1 After the plague, the Lord said to Moses and to Eleazar the son of Aaron, the priest, 2 “Take a census of all the congregation of the people of Israel, from twenty years old and upward, by their fathers' houses, all in Israel who are able to go to war.” 3 And Moses and Eleazar the priest spoke with them in the plains of Moab by the Jordan at Jericho, saying, 4 “Take a census of the people, from twenty years old and upward,” as the Lord commanded Moses.
After giving a few more examples of how the people of Israel disobeyed and failed to trust God, He once again calls on them to take a census. Those twenty and above were considered the new generation after the disobedient one had died in the wilderness. Comparing this census, or "Numbering," with the one made at the beginning of the wandering shows which tribes had decreased the most. For instance, the greatest decline was in the tribe of Simeon, which was especially noted in the chapter before this (ch.25) as those falling into Baal worship and being plagued because of it. Most of all, this chapter ends with the statement: 64 But among these there was not a man of those wo were numbered by Moses and Aaron the priest when they numbered the children of Israel in the Wilderness of Sinai. (except Caleb and Joshua). God had kept His promise. It was time to get ready to move on.