(Prabhupada's lecture - Śrīmad-Bhāgavatam 1.16.25 - Hawaii, January 21, 1974)
So satyaṁ śaucaṁ dayā. To accept guru, there is also service. And to give service to an inferior person who is suffering, that is also service. The one service is called dayā, and the other service is called sevā. So if you want to realize God, then the other service, sevā, not dayā. You cannot show your mercy to God. God is full. There is no need of your showing mercy. That sevā. Two kinds of service. One is called dayā, and another is called sevā. Sevonmukhe hi jihvādau svayam eva sphuraty adaḥ. If you want to know what is God, then the other service, sevā. Sevonmukhe hi jihvādau. And that service begins from the tongue.
Now, generally, when we think of service, we think of our hand and legs, that "By..., I can render service with my hands, with my legs." No. The science of understanding God—the service begins with the tongue. Just see. Ataḥ śrī-kṛṣṇa-nāmādi na bhaved grāhyam indriyaiḥ [Cc. Madhya 17.136]. You cannot understand what is God, what is Kṛṣṇa, His name, His activities, nāmādi... Nāmādi means name, form, qualities, activities, pastimes, entourage, so many things, ādi. Therefore... Just like we are chanting Hare Kṛṣṇa, but we cannot understand what is the meaning of Hare Kṛṣṇa. We cannot understand. Nāmādi. Na bhaved grāhyam indriyaiḥ. Indriyaiḥ means the senses. There are so many people are hearing this sound vibration, but why they're not becoming Kṛṣṇa conscious? Because there is no sevā, there is no service. Therefore it is said, ataḥ śrī-kṛṣṇa-nāmādi na bhaved grāhyam indriyaiḥ [Cc. Madhya 17.136]. But how it will be perceived by the indriyas? Sevonmukhe hi jihvādau. By service. And wherefrom the service begins? It begins jihvādau, beginning with the tongue, beginning with the tongue. This is the service.