Adam Clarke's Bible Commentary Verse 3. From twenty years old and upward] In this census no women were reckoned, nor children, nor strangers, nor the Levites, nor old men, which, collectively, must have formed an immense multitude; the Levites alone amounted to 22, 300. True-born Israelites only are reckoned; such as were able to carry arms, and were expert for war.
Matthew Henry Commentary
Verses 1-43 - The people were numbered to show God's faithfulness in thus increasin the seed of Jacob, that they might be the better trained for the war and conquest of Canaan, and to ascertain their families in order to the division of the land. It is said of each tribe, that those wer numbered who were able to go forth to war; they had wars before them though now they met with no opposition. Let the believer be prepared to withstand the enemies of his soul, though all may appear to be peace.
Original Hebrew מבן1121 עשׂרים6242 שׁנה8141 ומעלה4605 כל3605 יצא3318 צבא6635 בישׂראל3478 תפקדו6485 אתם853 לצבאתם6635 אתה859 ואהרן׃175