Joel 2:23

rejoice in the Lord--not merely in the springing pastures, as the brute "beasts" which cannot raise their thoughts higher (Isa 61:10; Hab 3:18). former rain . . . the rain . . . the former . . . the latter rain--The autumnal, or "former rain," from the middle of October to the middle of December, is put first, as Joel prophesies in summer when the locusts' invasion took place, and therefore looks to the time of early sowing in autumn, when the autumnal rain was indispensably required. Next, "the rain," generically, literally, "the showering" or "heavy rain." Next, the two species of the latter, "the former and the latter rain" (in March and April). The repetition of the "former rain" implies that He will give it not merely for the exigence of that particular season when Joel spake, but also for the future in the regular course of nature, the autumn and the spring rain; the former being put first, in the order of nature, as being required for the sowing in autumn, as the latter is required in spring for maturing the young crop. The Margin, "a teacher of righteousness," is wrong. For the same Hebrew word is translated "former rain" in the next sentence, and cannot therefore be differently translated here. Besides, Joel begins with the inferior and temporal blessings, and not till Joe 2:28 proceeds to the higher and spiritual ones, of which the former are the pledge.

— Jamieson-Fausset-Brown Commentary (public domain)