Anyone who gives spiritual instructions based on the revealed scriptures is accepted as a spiritual master. Although others give help in showing the way to beginners, the guru who first initiates one with the maha-mantra is to be known as the initiator, and the saints who give instructions for progressive advancement in Krsna consciousness are called instructing spiritual masters. The initiating and instructing spiritual masters are equal and identical manifestations of Krsna, although they have different dealings. Their function is to guide the conditioned souls back home, back to Godhead.
From Srila Prabhupada’s purport to Sri Caitanya-caritamrta Adi-lila 1.34