Guru Tattva

Must be uttama-adhikari who can never fall down
“One should not become a spiritual master unless he has attained the platform of uttama-adhikari .” (The Nectar of Instruction, text 5, purport)

“There is no possibility that a first-class devotee will fall down, even though he may mix with non-devotees to preach. Conviction and faith gradually increase to make one an uttama-adhikari, a first-class devotee.” (Sri Caitanya-caritamrta, Madhya-lila 22.71, purport)

Must be mahabhagavata
“When one has attained the topmost position of maha-bhagavata, he is to be accepted as a guru and worshipped exactly like Hari, the Personality of Godhead. Only such a person is eligible to occupy the post of a guru.” (Sri Caitanya-caritamrta, Madhya-lila 24.330, purport)

Must be liberated soul
“It is to be understood that the conditioned soul is tightly tied by the ropes of illusion. [...] Because the bound cannot help the bound, the rescuer must be liberated. Therefore, only Lord Krishna, or His bona fide representative the spiritual master, can release the conditioned soul.” (Bhagavad-gita As It Is 7.14, purport, 1972 ed.)

Does not deviate at all
“A bona fide spiritual master is in the disciplic succession from time eternal, and he does not deviate at all from the instructions of the Supreme Lord [...]”
(Bhagavad-gita As It Is, 4.42, purport)

Receives direct dictation from Lord Krishna
“A spiritually advanced person who acts with authority, as the spiritual master, speaks as the Supreme Personality of Godhead dictates from within. Thus it is not he that is personally speaking. When a pure devotee or spiritual master speaks, what he says should be accepted as having been directly spoken by the Supreme Personality of Godhead in the parampara system.”
(Sri Caitanya-caritamrta, Antya-lila 5.71, purport)

“You are correct when you say that when the Spiritual Master speaks it should be taken that Krishna is speaking. That is a fact. A Spiritual Master must be liberated.”
(Srila Prabhupada Letter, June 10th, 1969)

Prabhupada: “Yes, because a devotee always consults Krishna and He gives order.”
Interviewer: “It’s a more direct communication.”
Prabhupada: “Yes. And He gives order [...] Krishna will tell directly. A devotee always consults Krishna and Krishna tells him, “do like this.” Not figuratively [...] a devotee does not do anything without consulting Krishna.” (Interview, July 14th, 1976)

Always embraced by Krishna
“[...] 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. Such a personality is krsnalingita-vigraha—that is, he is always embraced by the Supreme Personality of Godhead, Krishna [...] He is the guru, or spiritual master, for the entire world, a devotee on the topmost platform, the maha-bhagavata stage, and a paramahamsa-thakura, a spiritual form only fit to be addressed as paramahamsa or thakura.” (Sri Caitanya-caritamrta, Madhya-lila 25.9, purport)

Resident of the spiritual world
“Unless one is a resident of Krishna Loka, one cannot be a Spiritual Master. That is the first proposition. A layman cannot be a Spiritual Master, and if he becomes so then he will simply create disturbance [...] So to summarize the whole thing, it is to be understood that a bona fide Spiritual Master is a resident of Krishna Loka.” (Srila Prabhupada Letter, June 10th, 1969)

Identified with God Himself
“`One should understand the Spiritual Master to be as good as I am,’ said the Blessed Lord [...] `the Spiritual Master is the sum total of all demigods.’ That is, the acarya has been identified with God Himself.” (Srila Prabhupada Lecture, February 1936)

Body is completely spiritual
“The spiritual master, or acarya, is always situated in the spiritual status of life. Birth, death, old age and disease do not affect him [...] therefore, after the disappearance of an acarya, his body is never burnt to ashes, for it is a spiritual body. The spiritual body is always unaffected by material conditions.” (Srimad-Bhagavatam 10.4.20, purport)

Empowered to act as he likes
“The conclusion is that a spiritual master who is authorized and empowered by Krishna and his own guru should be considered as good as the Supreme Personality of Godhead Himself. That is the verdict of Visvanatha Cakravarti: saksad-dharitvenasa. [...] As Hari is free to act as He likes, the empowered spiritual master is also free. As Hari is not subject to mundane rules and regulations, the spiritual master empowered by Him is also not subject.” (Sri Caitanya-caritamrta, Madhya-lila 10.136, purport)