Please accept my blessings. I beg to acknowledge receipt of your letter dated 15th May, 1970.
I know you are sincere servant of Krsna, so sometimes we may do something which is not very congenial, but Krsna is so kind that one who is engaged in His transcendental loving service is corrected immediately from within as Krsna is sitting within everyone's heart. So you have gone there with a great responsibility on behalf of Sri Caitanya Mahaprabhu, and try to convince people about the importance of Krsna Consciousness, that will make everything nice and in order.
You have asked some specific mantra; there is no other greater mantra than Hare Krsna. Srila Bhaktivinode says, "When I chant Radha Krsna or Hare Krsna all my dangers are gone immediately." So which other mantra can be more effective than Hare Krsna.
So far responsibility is concerned, there is an action in Bhaktirasamrta Sindhu to be executed by the devotee which is called Krsna arthe akhila cesta which means to take all kinds of responsibilities for Krsna's sake. Sometimes I also think that let me go back to Vrndavana, in that peaceful situation, to live without any responsibilities; still, in this old age, I take the responsibility of managing our quite a big Institution now, and I have to reply so many letters from different centers to give them instruction. As an old man I can take relief from this work immediately, but for Krsna's sake I am pulling on even though there is sometimes personal inconveniences. So let us act in that way all together for Krsna's sake.
Regarding using our Temple for marriage ceremonies for the Hindu community, if they contribute something to the Temple they can use the Temple and perform the marriage with their own priest, but we cannot take responsibility for marrying others who are not initiated by us.
I beg to thank you also for the nice picture. I have kept the picture on my table, it is very nice. May bless you Gopala Krsna.