To op: actually if you’re looking for short pithy sayings that express lubavitch philosophy I refer you to Hayom yom that does exactly that. If you want the Chabad handbook to Avodas Hashem, Tanya is the best place to start, which would be very timely actually.
Yesterday’s Hayom yom:
“There are three schools of thought:
1. The discipline of nullification of the material by indicating the repulsive and abhorrent nature of all that is bodily and material. This is the school of Mussar.
2. The school of recognition of the superiority of the “inner form”1 and the spiritual – the dimension of character-traits and intellectuality2 – and instruction as to how one may come closer to attaining these. This is the school of Chakira, philosophy.
3. The discipline of predominance of form over matter. This school teaches the unique quality of the material when it is purified, and the unique quality of “form” when integrated with the material; the two are to be so thoroughly fused that one cannot detect where either of them begins or ends – for “Their beginning is wedged into their end, and their end into their beginning.”3 The One G‑d created them both, and for one purpose – to reveal the light of Holiness of His hidden power. Only both of them together will complete the perfection desired by the Creator. This is the school of (the teachings/instruction of) Chassidus.4”