Bible Notes Online - Joel 2 - ESV
Commentary

v1-11: The devastation of God's judgment.

v1: Zion, in Jerusalem, is at the centre of events, God's "holy hill." In Amos 7.7-8, God set His plumbline in the midst of His people. 

v2-5: The effects of the locust-like army, as in 1.4. The apparent organisation is part of the terror.

v6-9: They keep formation; for those in the line of their attack, this is quite terrifying. They pour into the city, allowing no escape for its occupants.

v10-11: The army is identified as the Lord's. This is not because they are faithful believers, or even angels, but simply because all nations are subject to His control; Is 8.5-8; 37.26-27; Jer 32.28; the Assyrian and Babylonian armies were both subject to Him.

v12-17: The call to repentance.

v12: "With all your heart," for any repentance must be true repentance. Part of the problem with Israel was their superficial faith.

v13-14: The call to return to the Lord, depending on His mercy. The prophet declares that God is gracious and compassionate.

v15-17: Another trumpet call, see v1, this time to call the people to repent.

The prophet even suggests a prayer for those responding; a prayer about God's own testimony through His people. "Spare Your people, O Lord."  "Why should they say among the peoples,' Where is their God?'" 

v18-27: The Lord's faithfulness, promising marvellous things ahead.

v18-20: The Lord honours their repentance; He will be zealous; He will answer. Grain, new wine, and oil restored; matching 1.10. He will take away the shame they endured as the "object of scorn," see v17. The mighty army will be driven far away, the threat finished.

v21-24: Widespread restoration; open pastures and trees (1.19); beasts of the field (1.20); fig tree and vine (1.7); joy (1.12); threshing floors, with wheat and barley (1.11); the Lord has restored His land, through autumn and spring rains, promising and delivering great fruitfulness.

v25-27: Answering the devastation of 1.4; the thoroughness of the devastation is matched by the thoroughness of the restoration. The people will never again be put to shame, never again need to be restored.

v28-32: The promise of the Spirit on the children of Judah and Israel. This appears not to be dependent upon repentance, but rather presents unconditional promises. The blessing of the Spirit is not the restoration following previous judgments, but something new for the people of God.

Acts 2.16 suggests a partial fulfilment, and a fuller blessing is yet to be. The language of, for example, Matt 2.15 is more specific concerning fulfilled prophecy.

v28-29: "All people" refers, in context, to Judah and Israel; your sons and daughters, your old men and your young men, my servant, men and women. See 3.1, where the prophet refers to the restoration of Judah and Jerusalem.

v30-31: Signs before the day of the Lord, as in Matt 24.29-30. Here is warning of coming events.

v32: Salvation through calling on the name of the Lord. Irrespective of our understanding of the way this prophecy will be fulfilled, the glorious truth is that salvation is in 'the name of the Lord.'