The Rebbe said: Separating oneself from a tzaddik is like committing idolatry.

The only difference between the letters Dalet and Resh is a small protrusion. It is written in the holy Zohar that this protrusion is the tzaddik (Tikkuney Zohar #21, 55b, 58b). Separating oneself from a tzaddik separates the protrusion from the Dalet, making it into a Resh. The word EChaD (one) expresses God’s unity. Substitute a Resh for the Dalet in echaD and you have acheR (another). It is written, “You shall not bow down to another god” (Exodus 34:14). Remove the protrusion and the Dalet becomes a Resh – the echaD of God’s unity becomes the acheR of idolatry and atheism (see Baal HaTurim on Deuteronomy 6:4).

Faith in God comes through the true tzaddikim, who are the protrusion of the Dalet that expresses God’s unity (cf. Likutey Moharan I, 10:5).

In many places, the Rebbe says that the root of faith can be attained only through closeness to the tzaddikim.