But if you do not do so, then take note, you have sinned against the Lord; and be sure your sin will find you out.
Numbers 32:23, NKJV
Although the Lord had commanded Israel to conquer Canaan, the tribes of Reuben and Gad were proposing an alternative. Since the land east of the Jordan River was ideal for livestock raising, they wished to remain there and not cross the Jordan to fight the enemies of Israel.
To Moses, their reluctance to fight sounded like Kadesh Barnea all over again, so these two tribes promised to fight alongside the others, helping conquer territory west of the Jordan River that would never be theirs. Moses sternly warned them to honor their pledge. If they failed to obey God, their sin would find them out, and they would be punished accordingly.
So-called secret sins are truly exposed. To the only eyes that matter, there is no secret sin.