Srila Prabhupada : The practical example is here. These European and American boys are coming from well-to-do families. Why are they serving me? I am Indian, coming from a poor country. I cannot pay them. When I came to the West, I had no money. I brought only forty rupees. That was only an hour's expenditure in America. So their soul is to carry out my instruction. And therefore they are making progress. Pranipatena pariprasnena - they are asking questions. I am trying to reply to them, and they have all got full faith. They are serving like menial servants. This is the process.
If the spiritual master is bona fide and the disciple is very sincere, then the knowledge will be there. This is the secret. Yasya deve para bhaktir yatha deve tatha gurau [SU 6.23] - Vedic knowledge is revealed unto those who have faith in both the Lord and the spiritual master. Therefore in Vedic society, the students are automatically sent to the gurukula [the place of the spiritual master], regardless of whether one is a king's son or from some other background. Even Krishna had to go to gurukula.
There is a story that once Krishna went with a classmate to the forest to collect dry wood for His spiritual master. Suddenly there was a heavy rainstorm, and they could not get out of the forest. The whole night they remained in the forest with great difficulty. The next morning, the guru, their teacher, along with other students, came to the forest and found them. So even Krishna, whom we accept as the Supreme Lord, had to go to gurukula and serve the spiritual master as a menial servant.
So all of the students at the gurukula learn how to be very submissive and how to live only for the benefit of the guru. They are trained from the very beginning to be first-class submissive students. Then the guru, out of affection and with an open heart, teaches the boys all he knows. There is no question of money. It is all done on the basis of love and education.