John Gill Commentary Numbers 32:6

"And Moses said unto the children of Gad, and to the children of Reuben, Shall your brethren go to the war, and shall ye sit here?" — Numbers 32:6 (ASV)

And Moses said to the children of Gad, and to the children of
Reuben
Being displeased with their motion, as his following discourse shows, it having at first sight an appearance of covetousness and cowardice:

shall your brethren go to war, and shall you sit here?
it is not reasonable that your brethren should be left by you and engage in a war with your common enemies, to dispossess them of their land before they can settle in it and you remain here easy and quiet in the possession of a fruitful country.