Truth and Life are two things that a person wants by nature. If you were to offer somebody a perfect life on the condition that he would be put to sleep, he would be in a dream state for the rest of his life. He would have dreams and fantasies be put into his subconscious for the rest of his life. Who would ever agree to such a thing? Nobody. But why? it would be seemingly perfect. There are two problems with such an arrangement, it is not emes, truth, and it is not chaim, life. G-d is called both Truth and Life.
The Rebbe Rashab wrote "the 19th of Kislev...is a festival on which "He redeemed our soul in peace," and our soul's illumination and vitality were given to us, this day is Rosh Hashana for Chassidus bequeathed us by our sacred forebears, identical with the teachings of the Baal Shem Tov."
Light (Ohr) and liveliness (chayus).
Chassidus is that which gives us light which illuminates for us the truth of the world.
Chassidus also gives us liveliness (chayus) to live a life full of vitality.
Happy Yud Tes Kislev.