From the Bible:
Jesus emphasized the importance of having a teacher by asking John to baptize him. In the Gospel of St. Matthew, Chapter 3, we read of his coming to John. “Thus,” Jesus said to John, “it becometh us to fulfill all righteousness.”
From the Bhagavad Gita, fourth Chapter:
Open thyself to those who have attained wisdom. They will be thy teachers. Ask questions of them [both verbally and mentally]. Serve them faithfully, and with devotion.
How is the devotee to recognize one who has attained wisdom? The Bhagavad Gita gives us this inspiring description of the sage:
By this sign is he known,
Being of equal grace to comrades, friends,
Chance-comers, strangers, lovers, enemies,
Aliens and kinsmen; loving all alike,
Evil or good.
