Albert Barnes Commentary Joel 1:15

"Alas for the day! for the day of Jehovah is at hand, and as destruction from the Almighty shall it come." — Joel 1:15 (ASV)

Alas for the day! for the Day of the Lord is at hand – The judgment of God, then, which they were to seek to avert, was still to come: “All times and all days are God’s. Yet they are said to be our days, in which God leaves us to our own freedom, to do as we will, and which we may use to repent and turn to Him.” Thus Christ says, ‘O Jerusalem - if you had known in this your day the things which belong unto your peace’ (Luke 19:42).

“That time, on the contrary, is said to be God’s Day, in which He does any new, rare, or special thing, such as is the Day of Judgment or vengeance.” All judgment in time is an image of the Judgment for eternity.

“The Day of the Lord” is, then, each “day of vengeance in which God does to man according to His will and just judgment, inflicting the punishment which he deserves, as man did to Him in his day, manifoldly dishonoring Him, according to his own perverse will.” That Day “is at hand” and is to come suddenly. Speed then must be used to prevent it. It may be prevented by speedy repentance before it comes; but when it does come, there will be no avoiding it, for

As a destruction from the Almighty shall it come – The name “the Almighty” or “God Almighty” is rarely used in Holy Scripture. God revealed Himself by this Name to Abraham when renewing to him the promise, which was beyond nature, that he should be a father of many nations when he and Sarah were old and advanced in age. He said, I am God Almighty; walk before Me and be perfect (Genesis 17:1–6, 17:16-21; Genesis 18:10–14; Romans 4:17–21).

God Almighty uses it again of Himself in renewing the blessing to Jacob (Genesis 35:11); and Isaac and Jacob use it in blessing in His Name (Genesis 28:3; Genesis 43:14; Genesis 48:3; Genesis 49:25). It is not used as a mere name of God, but always in reference to His might, as in the book of Job which treats chiefly of His power. In His days of judgment God manifests Himself as the All-mighty and All-just.

Hence, in the New Testament, it occurs almost exclusively in the Revelations, which reveal His judgments to come. Here the words form a sort of terrible proverb, from where they are adopted from Joel by the prophet Isaiah (Isaiah 13:6). The word “destruction, שׁד shôd —” is formed from the same root as “Almighty, שׁדי shadday.” “It shall come as might from the Mighty.” Only, the word “might” is always used of “might” put forth to destroy, a “mighty destruction.” He says then, in fact, that that Day shall come, like might put forth by the Almighty Himself to destroy His enemies: irresistible, inevitable, unendurable, overwhelming the sinner.