The prophet urged the blowing of the shophar in Zion again, but this time to call a public assembly and a fast rather than to announce the coming invader ( Joel 2:1; cf. Joel 1:14). Fasting involved sacrificially going without food to devote oneself to a higher spiritual purpose. God"s people needed to gather together and Revelation -consecrate themselves to Him as a people. Everyone without exception should participate, from the oldest to the youngest. Even newlyweds, who sometimes received a special exemption for being newly wed ( Deuteronomy 24:5), needed to attend this meeting. [source][source][source]
It is interesting that the Jews will assemble in the Promised Land, having received encouragement from the Antichrist, during the first half of the Tribulation. Then the invader will descend on their land and the terrible prospect envisioned in Joel 2:1-11 will take place, in the second half of the Tribulation. Antichrist will persecute them. They will not assemble then in repentance, however. [source][source][source]