MISHNA: From when, i.e., from which date, does one begin to mention the might of the rains by inserting the phrase: He makes the wind blow and rain fall, in the second blessing of the Amida prayer? Rabbi Eliezer says: The phrase is inserted from the first Festival day of the festival of Sukkot. Rabbi Yehoshua says: From the last Festival day of the festival of Sukkot. Rabbi Yehoshua said to Rabbi Eliezer: Since rain is nothing other than a sign of a curse during the festival of Sukkot, as rainfall forces Jews to leave their sukkot, why should one mention the might of rain during this period? Rabbi Eliezer said to him: I too did not say that it is proper to request rain at this time, but it is proper only to mention the phrase: He makes the wind blow and rain fall, in its due time. Rabbi Yehoshua said to him: If so, i.e., if reciting the phrase does not constitute a request for rain, one should always mention rain, even in the summer. The mishna states a general principle: One requests rain only immediately preceding the rainy season. ...: One mentions the might of the rains and recites: He makes the wind blow and the rain fall in the second blessing of the Amida prayer, the blessing of the resurrection of the dead. And the request for rain: And grant dew and rain as a blessing, is recited in the ninth blessing of the Amida prayer, the blessing of the years...... It is written here: “Who does great things that are beyond comprehension,” and it is written there, with regard to the creation of the world: “Have you not known? Have you not heard that the everlasting God, the Lord, the Creator of the ends of the earth, does not grow faint or weary? His discernment is beyond comprehension” (Isaiah 40:28). This shows that both creation and rainfall are beyond comprehension.
...... Rabbi Yoḥanan said: There are three keys maintained in the hand of the Holy One, Blessed be He, which were not transmitted to an intermediary, i.e., God tends to these matters Himself. And they are: The key of rain, the key of birthing, and the key of the resurrection of the dead. Rabbi Yoḥanan cites verses in support of his claim. The key of rain, as it is stated: “The Lord will open for you His good treasure, the heavens, to give the rain of your land in its due time” (Deuteronomy 28:12), indicates that rainfall is controlled by God Himself.
Although there are countries where rain is necessary at the beginning of the winter, as it is in Eretz Israel and there are lands where rain is also needed after Pesach, the prayer for rain is added only from one of the two dates, either the 7th of Cheshvan or 60 days after Tekufat Tishrei. And it ends on the same date. Erev Pesach, everywhere.
Eliyahu Kitov
A day when rain falls is as great as the day on which heaven and Earth were created.
Rain falls only when Israel's sins are forgiven.
Great is the day when rain falls for even a small coin in one's pocket is blessed by it.
A day when rain falls is as great as the day of the in-gathering of the exiles. (Taanit 7b-8a)