Before the Lord — Before the ark, which was the token of God's presence. He alludes either to the order of the tribes in their march, whereby Reuben and Gad marched immediately before the ark, or to the manner of their passage over Jordan, wherein the ark went first into Jordan, and stood there while all the tribes marched over Jordan by and before it, and these amongst the rest, as is expressly noted in these very words, that they passed over before the Lord, Joshua 4:13.
Related Commentaries of Numbers 32:20
Numbers 32:20
20 And Moses said unto them, If ye will do this thing, if ye will go armed before the LORD to war,