Numbers 1:3

From twenty years old and upwards,.... All that had entered into their twentieth year, or, as it should rather seem, who were full twenty years of age, and all that were above it without any limitation; though some limit it to fifty, and others to sixty years, when men may be reasonably excused going to war; for to know who were fit for it seems to be a principal design of this order, as follows:

all that are able to go forth to war in Israel; who being about to journey, might expect to meet with enemies, with whom they would be obliged to engage in battle; and therefore it was proper to know their strength, and whom to call out upon occasion: Aben Ezra observes, that the phrase "in Israel" excepts the mixed multitude; those were not of Israel, and so not numbered, and perhaps not to be trusted or depended upon in war; nor were they mustered and marshalled by the standards of the several tribes; in a mystical sense, those numbered may signify the valiant of Israel, the same as the young men in 1 John 2:14; see Song of Solomon 3:7;

thou and Aaron shall number them by their armies; each tribe making a considerable army, Exodus 7:4; these people were now typical of the church of God in its militant state in the wilderness, for which they are provided, and prepared, and accoutred.