One must execute devotional service under the guidance of a devotee or directly under the guidance of the Supreme Personality of Godhead. It is not possible, however, to train oneself without guidance from the spiritual master.
In spiritual life, one must conduct one's whole life under the guidance of the guru. Only one who executes his spiritual life under the direction of the spiritual master can achieve the mercy of Krishna.
It is imperative that one approaches a spiritual master, for by such association one proportionately develops his consciousness towards the Supreme Personality of Godhead.
One has to ascertain the right path for his activities by following in the footsteps of great saintly persons and books of knowledge under the guidance of a spiritual master.
Whatever our destiny is, whatever our Karma is, if we simply accept the mercy of Guru, "Guru Kripa", it can completely liberate us from all of our previous Karmic bondage.
You can not understand "Scripture" without seeing through the eyes of the Spiritual Master or Advanced Devotees.