Joel 1:13 - Albert Barnes' Notes on the Bible

Gird yourselves - that is, with haircloth, as is elsewhere expressed Isaiah 22:12; Jeremiah 4:8; Jeremiah 6:26. The outward affliction is an expression of the inward grief, and itself excites to further grief. This their garment of affliction and penitence, they were not to put off day and night. Their wonted duty was to “offer up sacrifice for their own sins and the sins of the people” Hebrews 7:27, and to entreat God for them. This their office the prophet calls them to discharge day and night; to “come” into the court of the temple, and there, where God showed Himself in majesty and mercy, “lie all night” prostrate before God, not at ease, but in sackcloth. He calls to them in the Name of his God, “Ye ministers of my God;” of Him, to whom, whosoever forsook Him, he himself was faithful. : “The prophets called the God of all, their own God, being united to Him by singular love and reverential obedience, so that they could say, “God is the strength of my heart and my portion forever” Psalms 73:26. He calls Him, further, “their” God, (your God) in order to remind them of His special favor to them, and their duty to Him who allowed them to call Him “their” God.