Rashi on Numbers 32:17/רש"י על במדבר ל״ב:י״ז

1ואנחנו נחלץ חשים means, AND WE SHALL ARM OURSELVES SPEEDILY, the last word being the same as in (Isaiah 8:3): “the spoil hasteth, the prey speedeth (חש)” and in (Isaiah 5:19), “Let Him make haste, let Him speed."

2לפני בני ישראל BEFORE THE CHILDREN OF ISRAEL - i.e. at the head of the troops, because they were mighty men; for thus is it said of Gad, (Deuteronomy 30:20): “He teareth the arm, with the crown of the head”. Moses distinctly stated this to them in Sedrah אלה הדברים (Deuteronomy 3:18): “And I commanded you at that time … Ye shall pass over armed before the children of Israel, all ye men of valour”. And regarding the siege of Jericho it is written, (Joshua 6:13): “And the armed men (החלוץ) went before them”— this refers to the tribes of Reuben and Gad who thus fulfilled the conditions they had laid down.

3וישב טפנו AND OUR LITTLE ONES SHALL STAY, so long as we are with our brethren waging war,

4בערי המבצר IN THE FORTIFIED CITIES which we will now build (cf. v. 16 with v. 36).