John Gill's Bible Commentary Ver. 5. So they were delivered out of the thousands of Israel , etc.]] Several thousands very probably offered themselves voluntarily to go to the war, or however were summoned together on this account, and out of them the following number was delivered of picked and chosen men: a thousand [of every] tribe, twelve thousand armed for war ; which was but a small number to go against so considerable a nation and people; but this was done to show that the war was of the Lord, he would fight the battle, and give them victory, it being the same to him to do it with few as with many; and to encourage the people of Israel to believe the Lord would give them success against their many and powerful enemies in the land of Canaan, on the borders of which they now were.
Matthew Henry Commentary
Verses 1-6 - All who, without commission from God, dare to execute private revenge and who, from ambition, covetousness, or resentment, wage war an desolate kingdoms, must one day answer for it. But if God, instead of sending an earthquake, a pestilence, or a famine, be pleased to authorize and command any people to avenge his cause, such a commissio surely is just and right. The Israelites could show such a commission though no persons now can do so. Their wars were begun and carried of expressly by Divine direction, and they were enabled to conquer by miracles. Unless it can be proved that the wicked Canaanites did no deserve their doom, objectors only prove their dislike to God, an their love to his enemies. Man makes light of the evil of sin, but God abhors it. This explains the terrible executions of the nations whic had filled the measure of their sins.
Original Hebrew וימסרו4560 מאלפי505 ישׂראל3478 אלף505 למטה4294 שׁנים8147 עשׂר6240 אלף505 חלוצי2502 צבא׃6635