The First Month

Be glad then, ye children of Zion, and rejoice in the Lord your God: for he hath given you the former rain moderately, and he will cause to come down for you the rain, the former rain, and the latter rain in the first month. (Joel 2:23—KJV)
The former rain, and the latter rain in the first month.
Israel has two years that it celebrates. The first month of the religious year is Abib. This is the time of the Passover. In the month of Abib, Passover, Unleavened Bread, and Firstfruits are celebrated. These three observances symbolize the foundational work of the Christian redemption.
The first month of the business year is Tishri. The business year begins on the seventh month of the religious year, Abib.
It is my point of view that the"first month," of Joel 2:23, is referring to Tishri, the seventh month of the religious year.
The first day of Tishri is celebrated as the Blowing of Trumpets. To the present day, this is the Jewish New Year's day.
The Lord said to Moses,“Say to the Israelites: ‘On the first day of the seventh month you are to have a day of rest, a sacred assembly commemorated with trumpet blasts. Do no regular work, but present an offering made to the Lord by fire.’” (Leviticus 23:23-25)
The tenth of Tishri begins the Day of Atonement.
The fifteenth of Tishri begins the week of Tabernacles.
Such is the "first month" of Joel 2:23.