Isaiah 66:15

15.For, lo, Jehovah will come in fire. The object of this ( ὑποτύπωσις) lively description is, that believers, when they see worthless men laughing at their distresses, and growing more and more insolent, may not on that account turn aside from the right path, or lose courage; for he intended not only to smite wicked men, who are moved by no threatenings, and scorn all instruction, (225) but to comfort good men, that they may feel that they are happy, because they are under God’s protection; and may not attach themselves to the wicked on account of the prosperity of all their undertakings. Their advantage is, therefore, what he has chiefly in view, that they may be satisfied with God’s protection and grace. But it may admit of doubt whether or not he includes the last judgment, along with the temporal punishments with which he now begins to chastise the wicked. For my own part, I have no doubt that he intends to include that judgment also, along with those which were only the forerunners of eternal destruction.

Will come. This began to be accomplished, when, by carrying away the people to Babylon, God took vengeance on domestic foes. Next, when the time of the deliverance was accomplished, he attacked more severely the wicked Gentiles by an armed force, and ceased not to give other and various proofs of his approach, by which he shewed himself to be present with the elect people, and came in fire to judge their enemies. Lastly, we know that he will come in fire at the last day, to take vengeance on all the wicked. But this passage ought not to be limited to the last judgment, so as to include all the rest. Yet these threatenings, as we shall see soon afterwards, are especially directed by the Prophet against hypocritical Jews.

These metaphorical expressions are very customary in Scripture; for we could not comprehend this dreadful judgment of God in any other way than by the Prophets employing metaphors drawn from known and familiar objects. (2 Thessalonians 1:8; 2 Peter 3:7.) By means of them the prophets endeavor to make a deep impression on our senses, that, struck with the true fear of God, we may not envy the wicked, for whom such dreadful vengeance is prepared. Hence we see how trivial and useless are the speculations of the Sophists, who dispute about the refined nature and qualities of that fire; for the design of Scripture is to point out to us under figures the dreadful judgment of God, which otherwise we could not imagine or understand. This is still more evident from the word “sword,” in the following verse; for it conveys the same meaning.