Kommentar zu Wajikra 26:4

בעתם [THEN I WILL GIVE YOU RAIN] IN ITS SEASON — i. e. at times when the rain is “seasonable”, at such moments when people do not usually go out on journeys, as, for instance, in the nights preceding the Sabbaths (Friday nights) (Sifra, Bechukotai, Chapter 1 1; cf. Taanit 23a).

THEN WILL I GIVE YOUR RAINS IN THEIR SEASON. He mentioned the matter of rains first [of all the blessings] because if they come in their proper season, the air is pure and good and the springs and rivers are good [clear], and thus it [the rain] is a [prime] cause of physical health, and all produce will increase and be blessed by it, just as He said, and the Land shall yield her produce, and the trees of the field shall yield their fruit.¹In Verse 4 before us. Thus because of this [pure state of the environment] people do not become sick, and none shall miscarry, nor be barren,²Exodus 23:26. even among their cattle,³See Deuteronomy 7:14. and they will live out [the full extent of] their days.⁴See II Samuel 7:12. For when the material frame [of human beings] is large and healthy, they can continue [in health] as in the days of Adam.⁵Adam lived nine hundred and thirty years (Genesis 5:5). See Ramban ibid., on Verse 4, (Vol. I pp. 98-99). Thus this [blessing — the rains in their seasons] is the greatest of all blessings [and therefore it is given first place].
Now He said that the heavens will respond to the earth⁶See Hosea 2:23. with rains in their seasons, and the earth shall respond⁷See ibid., Verse 24. with its “produce”, which includes vegetation and all moving creatures — cattle, beasts, creeping things and fowl, as well as fish — for the term ha’aretz [“the earth” or “the land,” in and ‘the land’ shall yield her produce] includes the whole of the lower sphere [i.e., everything under the sphere of the moon], just as [in the verses]: In the beginning G-d created the heaven and ‘ha’aretz’ (the earth);⁸Genesis 1:1. See Ramban ibid., Verse 3 (Vol. I, p. 25) where he discusses this topic fully, and mentions also the verses cited in the following text. And the heaven and ‘ha’aretz’ (the earth) were finished;⁹Ibid., 2:1. and similarly, Praise the Eternal from ‘ha’aretz’ (the earth), ye sea-monsters and all deeps,¹⁰Psalms 148:7. and so also in most verses in Scripture [where this word occurs]. Thus all things created in the lower spheres are “the produce of the earth.”

ונתתי גשמיכם בעתם, "And I will provide your rains at their proper time." We must first understand why the verse commences with the letter ו seeing the verse is not preceded by another promise that this verse adds on to. If you accept my interpretation of the word תלכו itself being the promise in the last verse, there is no need to wonder about the letter ו at the beginning of this verse.