(Click to enlarge painting of Srila Prabhupada meeting Srila Bhaktisiddhanta for the first time)
Prabhupāda (speaking about his guru, Srila Bhaktisiddhanta): That is his blessing. He wanted; I tried. That's all. Whatever is being done, it is by his desire. Vaiṣṇava sata saṅkalpa. Whatever he desires, that is to be fulfilled. Yasya deve parā bhaktir yathā deve tathā gurau.
Therefore, full faith in guru, that is the prime factor of success. Not any other things, no qualification, no education, only staunch faith in guru. Yasya deve parā bhaktir yathā deve tathā gurau. Yasya prasādād bhagavat-prasādaḥ. This is the secret.
So whatever little success is there, that was only this qualification, that I wanted to serve him. That's all. Otherwise, there was no business of coming here at the age of seventy years.
(Srila Prabhupada Conversation, Los Angeles, June 10, 1976)