Prabhupada Letters :: 1967.

"Guru and Krishna are two parallel lines on which the spiritual express runs very smoothly. One minus the other is no good for the devotee. Anyone who talks of Krishna without service to Guru will not be successful."

Prabhupada Letters :: 1972.

"That is advancement, to stick tightly to the orders of the Spiritual Master। Because my Guru Maharaja ordered it, I am also ordering it. Go on preaching, spread this Krsna Consciousness all over the world."

Prabhupada Letters :: 1974.

"If the guru is a representative of the Supreme Lord in disciplic succession and the student is sincere, only then he can get him out of the clutches of the material energy."