Matthew Henry Commentary Deuteronomy 20:1-9

"When thou goest forth to battle against thine enemies, and seest horses, and chariots, [and] a people more than thou, thou shalt not be afraid of them; for Jehovah thy God is with thee, who brought thee up out of the land of Egypt. And it shall be, when ye draw nigh unto the battle, that the priest shall approach and speak unto the people, and shall say unto them, Hear, O Israel, ye draw nigh this day unto battle against your enemies: let not your heart faint; fear not, nor tremble, neither be ye affrighted at them; for Jehovah your God is he that goeth with you, to fight for you against your enemies, to save you. And the officers shall speak unto the people, saying, What man is there that hath built a new house, and hath not dedicated it? let him go and return to his house, lest he die in the battle, and another man dedicate it. And what man is there that hath planted a vineyard, and hath not used the fruit thereof? let him go and return unto his house, lest he die in the battle, and another man use the fruit thereof. And what man is there that hath betrothed a wife, and hath not taken her? let him go and return unto his house, lest he die in the battle, and another man take her. And the officers shall speak further unto the people, and they shall say, What man is there that is fearful and faint-hearted? let him go and return unto his house, lest his brethren`s heart melt as his heart. And it shall be, when the officers have made an end of speaking unto the people, that they shall appoint captains of hosts at the head of the people." — Deuteronomy 20:1-9 (ASV)

In the wars in which Israel engaged according to the will of God, they could expect Divine assistance. The Lord was to be their only confidence. In these respects, they were types of the Christian's warfare.

Those unwilling to fight were to be sent away. This unwillingness might arise from a man's outward circumstances. God would not be served by men forced against their will.

Your people shall be willing (Psalms 110:3). In running the Christian race and fighting the good fight of faith, we must lay aside everything that would make us unwilling.

If a man's unwillingness arose from weakness and fear, he was permitted to return from the war. The reason given for this is so that his brothers' hearts would not fail as well as his own. We must take care that we do not fear with the fear of those who are afraid (Isaiah 8:12).