This process of devotional service is taught by Caitanya Mahāprabhu. Not that very easily, "We have seen Kṛṣṇa or seen Rādhārāṇī in rāsa-līlā." No, not like that. Feel the separation. The more you feel separation from Kṛṣṇa, you should understand that you are advancing. Don't try to see Kṛṣṇa artificially. Be advanced in separation feeling, and then it will be perfect. That is the teachings of Lord Caitanya.
Because with our material eyes we cannot see Kṛṣṇa. Ataḥ śrī-kṛṣṇa-nāmādi na bhaved grāhyam indriyaiḥ (CC Madhya 17.136). With our material senses we cannot see Kṛṣṇa, we cannot hear about Kṛṣṇa's name. But sevonmukhe hi jihvādau, when you engage yourself in the service of the Lord . . .
Where the service begins? Jihvādau. The service begins from the tongue, not from the legs, eyes or ears. It begins from the tongue. Sevonmukhe hi jihvādau. If you begin service through your tongue . . . how? Chant Hare Kṛṣṇa. Use your tongue. Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare. And take Kṛṣṇa prasādam. The tongue has got two business: to articulate sound, Hare Kṛṣṇa, and take prasādam. By this process you'll realize Kṛṣṇa.