The children of Reuben passed over armed As they had engaged to do, Numbers 32:20-27, and Joshua 1:13. About forty thousand prepared for war It is likely that Joshua drew out this number only of chosen men; and left all the rest to take care of their families and flocks. Passed over before the Lord Having passed over the river, they stood in battle array before the ark, at the distance, probably, of two thousand cubits; or, in the presence of the Lord, as the expression, before the Lord, may mean, who observed whether they would keep their covenant with their brethren or not.
Related Commentaries of Joshua 4:12
Joshua 4:12-13
12 And the children of Reuben, and the children of Gad, and half the tribe of Manasseh, passed over armed before the children of Israel, as Moses spake unto them:
13 About forty thousand prepareda for war passed over before the LORD unto battle, to the plains of Jericho.