ותן טל ומטר לברכה
AND GIVE DEW AND RAIN FOR A BLESSING
Just as we specify all the kinds of produce that Hashem blesses upon us, so do we specify the wondrous means and causes of that blessing as well. Thus, in addition to the soil, we also mention and specify the dew and the rain that Hashem bestows לברכה, with the precise amount and abundance necessary for blessing. By specifying and asking for all of the details, we become more and more aware of the kindliness of Hashem, and that He is the source of all the blessings.