"Regarding your question of Paramatma: you are fortunate enough for your sincere service, Krishna as Paramatma Who is sitting within your heart is now dictating. Krishna is so kind that He wants to help us as Spiritual Master in two ways. He helps us from within as Caitya Guru and He expands Himself externally as Siksa Guru (as instructor) and diksa Guru (initiator). So the principle is that whatever you are instructed by the Caitya Guru internally may be confirmed by the instructor or initiator externally. Then your progress will be complete."
Srila Prabhupada Letter to Sivananda, 05-21-69
"Well initiation or no initiation, first thing is knowledge... knowledge. Initiation is formality. Just like you go to a school for knowledge, and admission is formality. That is not very important thing."
Srila Prabhupada Press Interview, 10-16-76, Chandigarh
"The initiating spiritual master (diksa-guru) shows his cause-less mercy by giving his disciples instructions in chanting the mantra. By so doing, he points the disciples in the direction of the truths pertaining to the Supreme Lord, Sri Krsna. I consider the numerous instructing spiritual masters (siksa-gurus) to be more important, for they show more mercy by training the sadhakas in all the essential aspects of sadhana-bhakti."
Srila Bhaktivinoda Thakur, Kalyana-kalpataru
"Prabhupada: "Then so siksa and diksa-guru... A siksa-guru who instructs against the instruction of spiritual, he is not a siksa guru. He is a demon. Siksa-guru, diksa-guru means... Sometimes a diksa-guru is not present always. Therefore one can take learning, instruction, from an advanced devotee. That is called the siksa-guru. Siksa-guru does not mean he is speaking something against the teachings of the diksa-guru/Acarya. He is not a siksa-guru. He is a rascal."
Srila Prabhupada Lecture on Bhagavad-gita 17:1-3, 07-04-74, Honolulu
"If one develops love for Krsna by Krsna conscious activities, one can know the Supreme Absolute Truth, but he who tries to understand God simply by logical arguments will not succeed, nor will he get a taste for unalloyed devotion. The secret is that one must submissively listen to those who know perfectly the science of God, and one must begin the mode of service regulated by the preceptor. A devotee already attracted by the name, form, qualities, etc., of the Supreme Lord may be directed to his specific manner of devotional service; he need not waste time in approaching the Lord through logic. The expert spiritual master knows well how to engage his disciple's energy in the transcendental loving service of the Lord, and thus he engages a devotee in a specific devotional service according to his special tendency. A devotee must have only one initiating spiritual master because in the scriptures acceptance of more than one is always forbidden. There is no limit, however, to the number of instructing spiritual masters one may accept. Generally a spiritual master who constantly instructs a disciple in spiritual science becomes his initiating spiritual master later on.
One should always remember that a person who is reluctant to accept a spiritual master and be initiated is sure to be baffled in his endeavor to go back to Godhead. One who is not properly initiated may present himself as a great devotee, but in fact he is sure to encounter many stumbling blocks on his path of progress toward spiritual realization, with the result that he must continue his term of material existence without relief. Such a helpless person is compared to a ship without a rudder, for such a ship can never reach its destination. It is imperative, therefore, that one accept a spiritual master if he at all desires to gain the favor of the Lord. The service of the spiritual master is essential. If there is no chance to serve the spiritual master directly, a devotee should serve him by remembering his instructions. There is no difference between the spiritual master's instructions and the spiritual master himself. In his absence, therefore, his words of direction should be the pride of the disciple. If one thinks that he is above consulting anyone else, including a spiritual master, he is at once an offender at the lotus feet of the Lord. Such an offender can never go back to Godhead. It is imperative that a serious person accept a bona fide spiritual master in terms of the sastric injunctions. Sri Jiva Gosvami advises that one not accept a spiritual master in terms of hereditary or customary social and ecclesiastical conventions. One should simply try to find a genuinely qualified spiritual master for actual advancement in spiritual understanding."
Caitanya-caritamrta, Adi lila 1:35
"One should not become a spiritual master unless he has attained the platform of Uttama-Adhikari. A neophyte Vaisnava, or a Vaisnava situated on the intermediate platform, can also accept disciples, but such disciples must be on the same platform and it should be understood that they cannot advance very well toward the ultimate goal of life under his insufficient guidance. Therefore, a disciple should be careful to accept an Uttama-Adhikari as a spiritual master."
Nectar of Instruction, Chapter 5
Bhaktivedanta Book Trust. HDG A.C. Bhaktivedanta Swami Srila Prabhupada.