I will show wonders in the heavens and in the earth: blood, fire, and pillars of smoke.
And I will show wonders in the heavens and in the earth,.... This, and what follow, refer to the prodigies seen in the air, and done in the earth, a little before the destruction of Jerusalem (r); when in the air were seen comets and blazing stars, particularly one in the form of a sword, hanging over Jerusalem, and appearances of armies engaged in battle...
And I will shew wonders in the heavens and in the earth, blood, and fire, and pillars of smoke. (s) He warns the faithful what terrible things would come, with the intent that they should not look for continual quietness in this world: and yet in all these troubles he would preserve them.
Peter settles the meaning for us: Pentecost fulfilled this word. The Spirit poured out then was no mere trickle as in the Old Testament days of judges and prophets, but a full stream, abundant and plentiful, the very gift the Prophet foretold for the last days of Messiah.
AI summary
Commenting on Joel 2:28-32