"Yaarof KaMatar Likchi Tizal KaTal Imrasi", let my lessons flow like rainfall, let my sayings drip like dew (Haazinu 32:2). The Torah is compared to rain and dew. Rashi explains that Tal everybody is always happy with the dew, unlike the rain, which people caught on the road and people who have valuable item outside that can get ruined, and not very happy about.
If so asks the Maskil L'Dovid why mention rain at all? Just compare the Torah to Tal. He answers that while dew may be pleasant, it is not enough to make plants and vegetation grow. The rain is a necessity that cannot be foregone and the same with the heavy doses of Torah that truly help us grow.
He also brings from the Arizal that basic understanding of Torah, the Pshat, is compared to Tal. This is for everyone to learn and grasp. Rain is a Mashal for the Sodos HaTorah, the secrets of the Torah that are not for everyone. Like getting caught in the rain if someone is not prepared or cutout for learning Kabala it can ruin him just like the wine in open pit when the heavy rains come down.
YH, 2009-09-25 13:25:34 Rabbi Chaim Vital writes in the name of the Arizal writes, "Mitzva l'galos zos ha'chochma" - It is a Mitzvah to reveal this wisdom. This means that although until the period of the Arizal, the Kabbalah was held only within a close circle, the time had come for the teachings of the Kabbalah to be taught widely. The Lurianic school of Kabbalah, which follows the teachings of the Arizal, and its disciples, revolutionized the Jewish world and popularized the study of Kabbalah. MG, Har Nof, 2009-10-06 15:40:08 What does it mean if rain falls during Sukkot?