The most important element in Bhakti yoga, or any genuine spiritual path, is to learn from a teacher who is pure. Pure teachers are rare, but we can learn how to recognize them and thus avoid being misguided. Such discretion is an important characteristic of progressive spiritual life.
Bhagavad-gita, Chapter Two, says that a pure teacher speaks exactly what God, Krishna, has taught, without change. He gives up all desire for personal gratification and wants only to please Krishna. He cannot give up, or be led away from, the Lord’s service even for a moment.
A person who attains this exalted level of Bhakti receives direct guidance from Krishna and displays all the qualities of a pure devotee.
The pure teacher controls his senses, acts always in Krishna consciousness, and has firm faith that devotional service to Krishna fulfills all obligations and includes all other goals.
The pure devotee of God is a teacher by example because his behavior and teachings are in perfect harmony. Such a person is an enlightened teacher (acharya), an instrument for Krishna’s work in the world.
To serve such a person is the path to enlightenment and liberation, and an absolute necessity for the proper execution of the Bhakti practice.
There are many enlightened teachers (acharyas) in the Bhakti line of the Hare Krishna movement. Some of the more prominent ones are Srila Prabhupada, Bhaktisiddhanta Saraswati Thakura, Bhaktivinoda Thakura, and Sri Chaitanya Mahaprabhu.