Ataḥ śrī-kṛṣṇa-nāmādi na bhaved grāhyam indriyaiḥ. In these blunt material senses you cannot understand what is this Hare Kṛṣṇa mantra. It requires purification of the senses, when you will understand what is Kṛṣṇa's name, nāmādi, what is Kṛṣṇa's form, what is Kṛṣṇa's quality, what is Kṛṣṇa's entourage, what is Kṛṣṇa's pastime. You cannot understand. How you will be understanding? Sevonmukhe hi jihvādau svayam eva sphuraty adaḥ. When you are engaged in the loving service of the Lord, beginning with your tongue, sevonmukhe hi jihvādau, by chanting this Hare Kṛṣṇa mantra and taking prasādam, in this way, gradually, when you will be purified, you will understand what is Kṛṣṇa. He will reveal. Kṛṣṇa reveals. Nāhaṁ prakāśaḥ sarvasya yogamāyā-samāvṛtaḥ (BG 7.25). For others, He is covered with yogamāyā's curtain, but for the devotees, He is open.
This is the secret. Vedeṣu durlabham adurlabham ātma-bhaktau (Bs. 5.33). If you simply study Veda, you will never be able to understand Kṛṣṇa. Therefore so many so-called Vedāntists, they do not know what is Kṛṣṇa. They consider Kṛṣṇa as ordinary human being. Avajānanti māṁ mūḍhā mānuṣīṁ tanum āśritam (BG 9.11). So the mūḍhas, the rascals, they cannot understand Kṛṣṇa. Only the devotees. Bhaktyā mām abhijānāti yāvān yaś cāsmi tattvataḥ (BG 18.55). If you want to understand Kṛṣṇa in truth, then you will have to accept this process, bhakti. Kṛṣṇa never says that "By jñāna, by yoga, by karma you can understand." No.