(Ibid. 12) "Always the eyes of the L-rd your G-d are in it (from the beginning of the year to the end of the year," i.e., for good), and elsewhere it is written (Psalms 104:32) "He looks to the earth and it trembles; He touches the mountains and they smoke." How are these verses to be reconciled? When Israel does the L-rd's will — "Always the eyes of the L-rd your G-d are in it," and they are not harmed.
When Israel do not do the L-rd's will — "He looks to the earth and it trembles; He touches the mountains and they smoke." Variantly: "Always the eyes of the L-rd your G-d are in it": sometimes for good; sometimes for ill. How so for good? If Israel were wicked on Rosh Hashanah and scant rain was decreed upon them (for the year), and they repented — to add to them (the rains) is impossible, for the decree has already gone forth; but the Holy One Blessed be He brings them down upon the land in their (optimum) time, when it is in need of them.
How so for ill? If Israel were absolutely righteous on Rosh Hashanah, and abundant rain was decreed upon them, and they repented (of their good) — to detract from them (the rains) is impossible, for the decree has already gone forth; but the Holy One Blessed be He brings them down upon the land, not in their (optimum) time, when it is not in need of them, upon deserts and seas, as it is written (Job 24:19) "Dryness, also heat, will steal from the days of snow.
They have sinned unto Sheol": What you have done against Me in the days of heat (i.e., at harvest time) — that you have not separated terumoth and tithes — will steal the rains from you.