The Lord shall go forth. The exhortation to "sing unto the Lord a new song" ends with Isaiah 42:12, and now the reason or groundwork for the exhortation has to be declared. God is about to make one of the great manifestations of his power upon the earth—to "go forth" against his enemies, and destroy and devour, and easily prevail against them—not, however, simply in the way of punishment and vengeance, but with a further merciful object.
He will punish Babylon, that he may deliver Israel. He has promised not to forsake his people (Isaiah 41:17). He is now about to give effect to his promise by a "new" and strange deliverance. He "will bring his people by a way that they knew not, and lead them in paths that they have not known" (Isaiah 42:16).
It has been said that "in effect it is the day of judgment which is here described" (Cheyne); but this seems to be only so far true as every manifestation of God's wrath towards his enemies is a foreshadowing of the great and awful day.
The event directly in view is the destruction of the Babylonian power by the irresistible arms of Cyrus. Hence the allusion to idolaters and images in Isaiah 42:17. As a mighty man … like a man of war.
(For similar anthropomorpbisms, see Exodus 15:3; Psalms 24:8.) He shall stir up jealousy; i.e. his own jealousy. God is "a jealous God" (Exodus 20:5), so much SO that his very "name is Jealous" (Exodus 34:14).
He is jealous for his own honour (supra, Isaiah 42:8), and jealous also for his people's honour and reputation and happiness. Occasionally he allows his jealousy to slumber (comp. Acts 12:1-25 :30, "The times of this ignorance God winked at"); and this he had now done for some fifty or sixty years, since his people were carried into captivity.
But the time of acquiescence has gone by—he is about to waken up his "smouldering jealousy, and stir it, till it burns up into a bright flame" (Delitzsch). He shall cry, yea, roar; rather, yea, shout; i.
e. utter his battle-cry with a clear, loud voice.