(Click to enlarge photo of Srila Prabhupada)
"There are different kinds of activities. So Kṛṣṇa says 'Whatever you do, it doesn't matter.' If somebody says that 'I am a businessman,' 'That's all right.' 'What is to be done?' 'Now, you do business to your best capacity, but the profit give to Me. The profit is Mine.' If you agree, then simply by doing business you become a great devotee. The same example: just like Arjuna. He is a fighter. So how he became so great devotee? By fighting. By fighting for whom? For Kṛṣṇa. 'No. He fought for getting the kingdom.' No, he did not fight for getting the kingdom. He said, 'Better I shall forego. I don't want this kingdom by fighting with my relatives.' He was very good man. But he agreed to fight for Kṛṣṇa. He changed his decision. Similarly, any work, if you do for Kṛṣṇa, that is bhakti. Don't think that bhakti means simply chanting Hare Kṛṣṇa and sitting down in one place. No. Bhakti means all kinds of activities. God is all-pervading; therefore bhakti is also all-pervading. From all spheres of life the devotional service can be done.
So these things are taught, those who are attached to work, for them; those who are attached to philosophy, for them; those who are attached to yoga system, for them; and those who are devotees, for them it is certainly. So from all angles of vision, when one comes to the point that kṛṣṇe bhakti kaile sarva-karma kṛta haya (CC Madhya 22.62), if one is engaged in the transcendental loving service of Kṛṣṇa, then everything is perfect. That is the conclusion of Bhāgavata. Svanuṣṭhitasya dharmasya saṁsiddhir hari-toṣaṇam (SB 1.2.13). You... How you can test that the particular engagement in which you are occupied, whether it is successful or not? How it is to be tested? The Bhāgavata gives you the formula. What is that, the formula? Now, saṁsiddhir hari-toṣaṇam (SB 1.2.13). You just try to see whether by your work Kṛṣṇa, the Supreme Lord, has become satisfied. If you see that He is satisfied, then whatever work you are doing, either you are philosopher or a businessman or a scientist, or anything, politician... There are so many occupational duties. But you have to test whether that is giving you real perfection. That test is that you have to see whether by your activity the Supreme Lord is satisfied. Then...
This is a great science. This is Kṛṣṇa consciousness science. Simply... Therefore we have to take shelter of an expert. Just like a student goes to a school, and if he works on exercises and he puts before the teacher, and if the teacher says, 'Yes, it is good,' then he is successful; similarly, tad-vijñānārthaṁ sa gurum evābhigacchet (MU 1.2.12), you have to approach to a guru or representative of Kṛṣṇa, and if he says, 'It is all right,' then you know that Kṛṣṇa is satisfied. Yasya prasādād bhagavat-prasādaḥ... You have to approach such a person whose certificate will ensure that Kṛṣṇa will be satisfied. You have to find out such person. Then your life is success. So that will also... You will get according to your sincerity of purpose, because Kṛṣṇa is within you."
(Srila Prabhupada Lecture, Montreal, July 2, 1968)