"Guru and Krishna are two parallel lines on which the spiritual express runs very smoothly. In the Chaitanya Charitamrta it is said 'Guru Krsna prasade paya bhakti lata bija.' By the Grace of Guru one gets Krishna and by the Grace of Krishna one gets a bona fide Guru. Therefore Krishna consciousness means staunch faith both in Guru and Krishna. One minus the other is no good for the devotee. So your faith in the principles of devotion to Guru will certainly help you more and more Krishna. Do not ever try to approach Krishna directly. Anyone who talks of Krishna without service to Guru will not be successful. So your faith in Guru and Krishna simultaneously will help you to become crowned with success in the progressive march in Krishna consciousness. Do not be worried, be situated in the present aptitude and everything will be clear."
(Srila Prabhupada Letter, September 27, 1967)
"As I have repeatedly said, that Krishna Consciousness is developed by following two parallel lines, means service of Krishna, and service of the Spiritual Master. This is the secret of success. The Spiritual Master must be bona fide, that is, he must come down from a bona fide Spiritual Master and must act according to the directions of the Spiritual Master, and by doing so, he gives proper directions about Krishna and the devotees serve Krishna under the direction of such Spiritual Master, and Krishna accepts service, and in this way the whole thing becomes beautiful and successful."
(Srila Prabhupada Letter, February 20, 1968)