Be An Emissary of HaShem!
It is imperative that every Jew know that he is an emissary of the Master of all, charged with the mission - wherever he may be of bringing into reality HaShem's will and intention in creating the universe, namely, to illuminate the world with the light of Torah and the service of HaShem. This is done through performing practical mitzvot and implanting in oneself fine character traits. -The Lubavitcher Rebbe (Hayom Yom 7 Adar I)The Key to Chassidus
The Gate of Unity - Shaar HaYichud
An audio class on Shaar HaYichud - The Gate of Unity of the Mittler Rebbe