It is known from the words of Chazal (see Pesachim 117a) that the Shechinah does not rest other than via the simchah of a mitzvah. Accordingly, every single person has the obligation to increase in the service of Hashem with joy, and even more so, to distance himself from depression, Rachamana litzlan, as happens with all illnesses, may H'shem have mercy upon us. Rather, we should fulfill the words of the pasuk (Tehillim 100:2-3), “Ivdu es H'shem b’simchah” (“Serve Hashem with joy”), for then we will merit “De’u ki Hashem Hu Elokim, Hu asanu v’lo anachnu” (“Know that H'shem is G-d; He made us, and to Him we belong”). We will also merit the sweetening of the judgments and be saved from all trouble, distress, affliction and illness, with Hashem’s help. And as is explained at length in the name of the holy
Baal Shem Tov, zy”a, as soon as a person who is going through a time of trouble recognizes that “achein Atah Keil mistateir” (“indeed, You are the GD Who conceals Himself”), it is no longer a concealment and nispardu “kol po’alei aven” (“all of the evildoers are scattered”).
In the holy sefer
Noam Elimelech (Parshas Va’eira s.v. “O Yomar”) it is written: “The rule is that when one wants to subdue the klipah the person must be happy, because then there can be no melancholy or sorrow. For when this one rises, the other one falls.”
Similarly, the holy Rebbe of Barditchev, zy”a, wrote in his sefer Kedushas Levi (Parshas Vayeitzei s.v. “Vayar V’hinei B’eir”): “It is known that H'shem always desires to bestow goodness upon His nation of Yisrael, but k’vayachol the sitra achara inhibits the flow of abundance. However, when the Yidden awaken themselves with simchah, it pushes away the chitzonim from being able to withhold the abundance. Then H'shem, with His great mercy and kindness, bestows an abundance of brachah on His nation Yisrael.”
The Belzer Rebbe Comforts Klal Yisrael
By Ami Magazine 2020