Learning Chassidus: obligatory for this generation!

...the main thing is that in our generations the study of Pnimiyus Hatorah is obligatory; not only this, but the lack of this learning G-d forbid delays the Geulah, as stated in the words of both the Alter Rebbe and the Gaon of Vilna...

Letter of the Lubavitcher Rebbe, 5721 (1961), Igros Kodesh v. 20, p.84