Jamieson, Fausset and Brown on Joel 1:13

13. Gird yourselves--namely, with sackcloth; as in Is 32:11, the ellipsis is supplied (compare Jr 4:8).

lament, ye priests--as it is your duty to set the example to others; also as the guilt was greater, and a greater scandal was occasioned, by your sin to the cause of God.

come--the Septuagint, "enter" the house of God (compare Joe 1:14).

lie all night in sackcloth--so Ahab (1Ki 21:27).

ministers of my God--(1Co 9:13). Joel claims authority for his doctrine; it is in God's name and by His mission I speak to you.