C. F. Keil and Franz Delitzsch on Joshua 22:20

Jos 22:20

He finally reminded them of the sin of Achan, how that had brought the wrath of God upon the whole congregation (Josh 7); and, moreover, Achan was not the only man who had perished on account of the sin, but thirty-six men had fallen on account of it at the first attack upon Ai (Jos 7:5). The allusion to this fact is to be understood as an argument a minori ad majus, as Masius has shown. “If Achan did not perish alone when he committed sacrilege, but God was angry with the whole congregation, what think ye will be the consequence if ye, so great a number, commit so grievous a sin against God?”