‘Yaarof kamatar likchi tizal katal imrasi’ - My torah should flow like the rain and the dew. Rashi explains that rain is not good for everyone so it says dew which is good for everyone. So why then, does it say rain at all?

Rain comes down forceful and abundant but not every plant can handle it, some break, some drown.  Dew, on the other hand, clings to each leaf and gently nourishes all. We see how first the Torah came like rain to our avos and leaders who were strong and capable. This would not have been good for all of klal yisrael, and so we see after the initial delivery to the avos and leaders, the Torah was delivered to the rest of Klal Yisrael as dew.