Adam Clarke on Joel 1:14

Call a solemn assembly - עצרה atsarah signifies a time of restraint, as the margin has it. The clause should be translated - consecrate a fast, proclaim a time of restraint; that is, of total abstinence from food, and from all secular employment. All the elders of the land and the representatives of the people were to be collected at the temple to cry unto the Lord, to confess their sins, and pray for mercy. The temple was not yet destroyed. This prophecy was delivered before the captivity of Judah.