Albert Barnes Commentary Haggai 2:1

"In the seventh [month], in the one and twentieth [day] of the month, came the word of Jehovah by Haggai the prophet, saying," — Haggai 2:1 (ASV)

In the seventh month, on the twenty-first day of the month—This was the seventh day of the Feast of Tabernacles (Leviticus 23:34; Leviticus 23:36; Leviticus 23:40–42), and its conclusion. The eighth day was to be a Sabbath, with its “holy convocation,” but the commemorative feast—the dwelling in booths in memory of God’s bringing them out of Egypt—was to last seven days.

The conclusion of this feast, then, could not fail to revive their sadness at the glories of their first deliverance by God’s “mighty hand and outstretched arm,” and their present small numbers and poverty. This depression inevitably brought with it heavy thoughts about the work in which they were engaged in obedience to God, all the more so because Isaiah and Ezekiel had prophesied of the glories of the Christian Church under the symbol of the temple.

Haggai is sent to relieve this despondency, plainly acknowledging the reality of its current basis, but renewing, on God’s part, the pledge of the glories of this second temple, which were to come.