Regarding your question about faith in devotees, faith must be there. But we should always take instruction from devotees who are considered to be elevated. A preacher's position is like this: He should have firm faith and love for Krishna. He should make friendship with devotees. He should be very much charitable and kind to the neophytes and he should avoid the company of nondevotees.
Letter to Hamsaduta, 28 September, 1969
So you have scientific mind and you want to use it in the service of Krsna. This is very good, and this I want that scientists step forward and preach Krsna consciousness. We are not preaching something fanaticism nor dry philosophy. Krsna consciousness is jnanam and vijnanam, practical knowledge. So I have given all the points in my books, and you should read them thoroughly.
Letter to Bhakta Dennis, 25 September, 1974
Regarding against propoganda, it is going on practically everywhere, especially Bengal. So we have to work very sincerely and Krishna will give us protection. The only hope, we can understand that demons are disturbed. That is quite natural. When Krishna was born, from the day of His birth, the demons wanted to kill him in so many ways but practically it was found that demons were killed by Krishna and He established His mission yada yada hi dharmasya glanir bhavati bharata/ abhyutthanam adharmasya tadatmanam srjamyaham [Bg. 4.7]. So if we work sincerely, the Krishna Consciousness Movement is non-different from Krishna. As Krishna killed all the demons, we should also be able to kill all demons if we remain faithful in the discharge of our mission.
Letter to Yasomatinandana, 24 September, 1976
Now I can understand that this Bhagavata-dharma discourse can be held anywhere all over the world and people will come in large numbers such great distance and under all kinds of hardships just to hear our discourse.
Letter to Kirtanananda, 23 September, 1972
I am pleased to note your attitude regarding business. Our policy is nirbandhe krishna sambandha: We shall accept all kinds of civil activities, including business, trade, industry, only in connection with Krishna. I am glad that you are following this principle, and Krishna will be very, very pleased upon you to make you advance in Krishna Consciousness.
Letter to Gargamuni, 22 September, 1969
You have both been very nice devotees and I would like you both to continue to make nice advancement. So please patch up any crack that may have come between yourself and ISKCON. As husband and wife you must always remain together and raise your daughter in Krishna Consciousness. I would like you to go back to New Vrndavana and fix up a nice living place for yourselves and help to develop the New Vrndavana scheme. Our ISKCON should be taken as being a family based upon love and trust, so as the father becomes unhappy when one of his children wishes to break family connections I also become unhappy when there is difficulties within our ISKCON family. So please do not consider leaving as you are spiritual children of mine.
Letter to Isana, Vibhavati, 21 September, 1970
Our relationship is eternal. But if somebody lags behind, so in spite of our eternal relationship one may not meet other at the destination. Just like a flock of birds - although very intimately related, everyone of them has to fly in the sky by individual strength. If one is less strong, the other cannot keep him in the sky. That is the law of nature. So long everyone of us is strong in Krishna Consciousness, there is no doubt, you can fly in the spiritual sky and meet together without failure. Therefore, individual strength is most important. And that individual strength is achieved in the association of devotees also.
Letter to Satsvarupa, 20 September, 1968
I am glad that Kulasekhara has come back. I think he cannot go from our society because he has already rendered some service to Krishna. So Krishna is not going to leave him at any cost. So treat him nicely so that he can be fixed up there. And his attention should be in the matter of painting. That's a very nice idea. Please offer my blessings to him, and treat him very well.
Letter to Hamsaduta, 19 September, 1968
The GBC authority must be accepted under all circumstances, not that there will be fighting amongst you. This fighting spirit will destroy everything, but what can I do, you American and European boys are trained up in this fighting attitude. Now put it aside and simply work cooperatively for spreading this movement all over the world. The standards I have already given you, now try to maintain them at all times under standard procedure. Do not try to innovate or create anything or manufacture anything, that will ruin everything. Simply do as I am doing and be always serious and sincere to serve Krsna, and He will give you intelligence how to do everything.
Letter to Bali-mardana and Pusta Krsna, 18 September, 1972
Regarding your invitation to take instruction from the University scholars, we are not concerned with a scholar who knows theoretically Caitanya Vaisnava Movement but we are interested with persons who are actually devotees who actually chant Hare Krsna Mahamantra and follows the regulative principles; Theoretical knowledge will not help us.
Letter to Jagadisa, 17 September, 1970