John Calvin Commentary Isaiah 42:13

"Jehovah will go forth as a mighty man; he will stir up [his] zeal like a man of war: he will cry, yea, he will shout aloud; he will do mightily against his enemies." — Isaiah 42:13 (ASV)

Jehovah like a giant. What Isaiah now adds is intended to overcome the temptations of believers. He ascribes strength and power to God, so that they may know that they will find a sure defense in Him; for in adversity we are perplexed, because we doubt whether or not God will be able to give us assistance, especially when by delaying He appears in some measure to reject our prayers. Therefore, the Prophet loudly extols the power of God, so that all may learn to rely on Him and place their confidence in Him.

Will go forth. The going forth that is mentioned here must be taken metaphorically, for God seemed to be concealed at the time when He permitted His people to be afflicted and oppressed without any sign of help. Therefore, the word means 'to come forth publicly for the sake of giving assistance.' This is confirmed by what follows.

And as a warrior. When he attributes burning indignation to God, with which He rushes forth like a warrior against His enemies, the comparisons are drawn from human feelings and declare to us the powerful assistance of God, which would not otherwise make a sufficiently powerful impression on our minds.

He therefore accommodates Himself to our understanding, as we have often said. This is so that we may know how ardently He desires to preserve us, how much He is distressed by the affliction and oppression of believers, and likewise how terrible His anger is whenever He prepares Himself for battle.

We should always observe that particular time which the Prophet had in view, to which these predictions must be applied. For while the enemies were becoming increasingly fierce and were taunting a suffering people, it was the duty of believers to look at something quite different from what they saw with their eyes. They needed to believe that God is sufficiently powerful to subdue their enemies and rescue them from their hands.

Nor was it only during the captivity that it was important for them to have their sorrow alleviated by this promise, but almost until the coming of Christ. This was because they were continually and painfully forced to encounter severe distresses, as is evident from history.