"The boys and girls in London are doing very nicely. My Guru Maharaja sent one sannyasi, Swami Bon Maharaja, to preach Krishna Consciousness in London, sometimes in 1933. Although he tried for three years and at the expense of my Guru Maharaja, he could do not do any appreciable work. So Guru Maharaja, being disgusted, called him back. In comparison to that situation, our 6 young boys and girls are neither very much advanced in their study of Vedanta nor any other Vedic literature, neither are they sannyasis. But still they are doing more tangible work than what Bon Maharaja could do there 35 years ago.
This very fact confirms the statement of Lord Caitanya that a preacher or teacher may be a householder, a sannyasi, a brahmana, a sudra, or anyone, provided he knows the science of Krishna. And to know the science of Krishna means to serve Krishna under the directions of a bona fide Spiritual Master. When we serve Krishna in this way, Krishna is pleased to reveal Himself. So we should follow strictly the Vedic principle that anyone who has unflinching faith in Krishna and the Spiritual Master, to him only the science of Krishna Consciousness becomes revealed. Then when we are fully conversant in revelation of Krishna Consciousness, we can meet any opposing elements and come out victorious."
A.C. Bhaktivedanta Swami Srila Prabhupada
Ref. VedaBase => Letter to: Hayagriva -- Los Angeles 31 January, 1969