Now, one may question, 'Whether you have seen Kṛṣṇa?' So how Kṛṣṇa can be seen? Yes. A spiritual master must have seen Kṛṣṇa. Without seeing, he cannot be spiritual master. But how Kṛṣṇa can be seen? Kṛṣṇa can be seen by love. Premāñjana-cchurita-bhakti-vilocanena (BS 5.38). Premāñjana-cchurita-bhakti-vilocanena santaḥ sadaiva hṛdayeṣu vilokayanti. Just like if you are in love with somebody, you can see him constantly—he is always on your eyes, anyone you love—so similarly, Kṛṣṇa also can be seen by development of love. Otherwise how we can see Kṛṣṇa? He is so great, unlimited. Your eyes, your senses, are all limited. You cannot see the unlimited by your limited sense perception. But you can see... Not you can see, but svayam eva sphuraty adaḥ. When you are developed in the sense of love of Godhead, then He reveals unto you. Therefore you can see.
Just like the sun. You cannot see the sun by challenge at night. If somebody says, 'Come on. I shall show you. See. Take some aeroplane,' what he will see? He can travel all the sky; still, he cannot see the sun. Similarly, this is an example. At night you cannot see the sun, but when the sun rises, you can see the sun, you can see yourself also. By seeing sun, you can see yourself, you can see the world. Similarly, when you see Kṛṣṇa, then you see everything.
Without seeing Kṛṣṇa, your eyes are blind, your senses are imperfect. Therefore it is said that 'Self-realized soul can impart knowledge unto you because he has seen the truth.'"
(Srila Prabhupada Lecture, Los Angeles, January 12, 1969)