The spiritual master and Krishna are two parallel lines. The train, on two tracks, moves forward. The spiritual Master and Krishna are like these two tracks. They must be served simultaneously. Krishna helps one to find bona fide Spiritual Master and bona fide Spiritual Master helps one to understand Krishna. If one does not get bona fide Spiritual Master, then how he can ever understand Krishna ? You cannot serve Krishna without Spiritual Master, or serve just Spiritual Master without serving Krishna. They must be served simultaneously.
First birth is from your parents, but real birth, real life, begins when one accepts a bona fide spiritual master and renders service unto him. Then the path is open for going back to home, back to Godhead, to live eternally in full knowledge and full bliss and in association with the Supreme Personality of Godhead Himself, Lord Krishna.
A devotee should be fixed in the conclusion that, the spiritual master cannot be subject to criticism and should never be considered equal to a common man.
Only an empowered personality can distribute the holy name of the Lord and enjoin all fallen souls to worship Krishna. By distributing the holy name of the Lord, he cleanses the hearts of the most fallen people. Therefore he extinguishes the blazing fire of the material world. Not only that, he broadcasts the shining brightness of Krishna's effulgence throughout the world. Such an acarya, or spiritual master, should be considered nondifferent from Krishna-that is, he should be considered the incarnation of Lord Krishna's potency.
The spiritual master can instruct the disciple though many different formats.
When the teacher, the spiritual master, is praying for the mercy of the Lord to enlighten the student, then by the blessings of the Lord the student gets the blessing of knowledge.