The following is a freely-translated excerpt from a letter by the Rebbe dated Purim, 5704 (1944):1
...There are several approaches to the endeavor of influencing one's fellow and bringing him closer to Torah and the observance of mitzvot. Generally speaking, there are two basic methods:
a) To describe to him the lowliness of man, the abhorrence and despicability of evil, the punishments of purgatory, etc. In other words, the emphasis is on what should be avoided. Basically, this is the approach of mussar (rebuke).
b) To explain and expound upon the greatness of the Creator, the immensity of His works, the immeasurable loftiness of Torah and mitzvot, and the like. In other words, the emphasis is on what it is that one should bring oneself closer to. Basically, this is the approach of Chassidism.
One of the differences between these two approaches:
When one's efforts to influence one's fellow concentrate on matters of the first category--how terrible and bitter is the lot of the sinner, how lowly is the person who lusts after the pleasures of the material world, and the like--the only positive aspect of the discussion is the hope that this might cause one's fellow to resume the right path. Aside from this hope, the discussion of these matters is not, in and of itself, a mitzvah.
On the other hand, the discussion of the concepts of the second category--understanding the processes of creation, "Know the G-d of your fathers,"2 appreciating the unity of G-d--is itself a mitzvah, independently of its potential to influence one's fellow...
