There is a famous drush that is brought by Nefesh haChayim in the beginning of the 4th chapter of shaar 1, and also discussed in Ruach Chayim. The mishnah in Pirkei Avos 2:1 says da ma lemaaleh mimeka (know what is above you), and Nefesh haChayim suggests to read "know that what is above -- is from you," i.e., that you are the source of the changes that take place in the spiritual worlds.
A similar take is attributed to Ba'al Shem Tov.
I have heard that the original source for the drush is Megaleh Amukos, but could not find it there. Would anyone know if that is really the source (and if so, where it is in the sefer), or there is an earlier work which brings it down?
Thank you so much!