| Barnes' Notes on the Bible The prophet uses words familiar to the people, and connected with several great deliverances (see the marginal references).
Clarke's Commentary on the BibleFor the battle is not yours, but God's - God will not employ you in the discomfiture of this great host; he himself will take the matter in hand, deliver you, and destroy them.
Gill's Exposition of the Entire BibleAnd he said, hearken ye, all Judah, and ye inhabitants of Jerusalem, and thou King Jehoshaphat,.... There is a climax or gradation in these words rising from the lowest to the highest; from the people of the cities in the country, to the inhabitants of Jerusalem the metropolis, and from thence to the king the supreme governor: thus saith the Lord unto you, be not afraid, nor dismayed, by reason of this great multitude; whose numbers were discouraging to the king, and he had taken notice of them, which this respects: for the battle is not your's, but God's: the cause was his, and he would espouse and maintain it; not they, but he, would fight the battle, and therefore they had nothing to fear.
Keil and Delitzsch Biblical Commentary on the Old TestamentJehaziel announced to the king and people that they need not fear before the great multitude of their foes; "for the war is not yours, but Jahve's," i.e., you have not to make war upon them, for the Lord will do it; cf. 1 Samuel 17:47.
Geneva Study BibleAnd he said, Hearken ye, all Judah, and ye inhabitants of Jerusalem, and thou king Jehoshaphat, Thus saith the LORD unto you, Be not afraid nor dismayed by reason of this great multitude; for the {k} battle is not yours, but God's. (k) They fight against God and not against you, therefore he will fight for you.
Wesley's Notes 20:15 But God's - God will fight for you, and he alone will do the work, you need not strike a stroke.
Matthew Henry's Concise Commentary20:14-19 The Spirit of prophecy came upon a Levite in the midst of the congregation. The Spirit, like the wind, blows where and on whom He listeth. He encouraged them to trust in God. Let the Christian soldier go out against his spiritual enemies, and the God of peace will make him more than a conqueror. Our trials will prove our gain. The advantage will be all our own, but the whole glory must be given to God.
Matthew Henry's Whole Bible CommentaryVerses 14-19 We have here God's gracious answer to Jehoshaphat's prayer; and it was a speedy answer. While he was yet speaking God heard: before the congregation was dismissed they had assurance given them that they should be victorious; for it is never in vain to seek God. 1. The spirit of prophecy came upon a Levite that was present, not in any place of eminency, but in the midst of the congregation, v. 14. The Spirit, like the wind, blows where and on whom he listeth. He was of the sons of Asaph, and therefore one of the singers; on that office God would put an honour. Whether he was a prophet before this or no is uncertain, most probably he was, which would make him the more regarded. There needed no sign, the thing itself was to be performed the very next day, and that would be confirmation enough to his prophecy. 2. He encouraged them to trust in God, though the danger was very threatening (v. 15): "Be not afraid; you have admitted fear enough to bring you to God, do not now admit that which will drive you to God, do not now admit that which will drive you from him again. The battle is not yours; it is not in your own strength, not for your own cause, that you engage; the battle is God's: he does and will, as you have desired, interest himself in the cause." 3. He gives them intelligence of the motions of the enemy, and orders them to march towards them, with particular directions where they should find them. To-morrow (the day after the fast) go you down against them, v. 16, 17. It is fit that he who commands the deliverance should command those for whom the deliverance is to be wrought, and give the necessary orders, both for time and place. 4. He assures them that they should be, not the glorious instruments, but the joyful spectators, of the total defeat of the enemy: "You shall not need to strike a stroke; the work shall be done to your hands; only stand still and see it," v. 17. As Moses said to Israel at the Red Sea (Ex. 14:13), "God is with you, who is able to do his work himself, and will do it. If the battle be his, the victory shall be his too." Let but the Christian soldier go out against his spiritual enemies, and the God of peace will tread them under his feet and make him more than a conqueror. 5. Jehoshaphat and his people received these assurances with faith, reverence, and thankfulness. (1.) They bowed their heads, Jehoshaphat first, and then all the people, fell before the Lord, and worshipped, receiving with a holy awe and fear of God this token of his favour, and saying with faith, Be it unto us according to thy word. (2.) They lifted up their voices in praise to God, v. 19. An active faith can give thanks for a promise though it be not yet performed, knowing that God's bonds are as good as ready money. God hath spoken in his holiness; I will rejoice, Ps. 60:5. | 
