Srila Prabhupada

Caitanya Mahāprabhu, He introduced. Saṅkīrtanaika-pitarau. Gaura and Nityānanda is the father of the saṅkīrtana movement. Therefore Vṛndāvana dāsa Ṭhākura has offered his prayer, saṅkīrtanaika-pitarau ājānu-lambita-bhujau kanakāvadātau, saṅkīrtanaika-pitarau kamalāyatākṣau (CB Ādi-khaṇḍa 1.1), vande mahā-puruṣa te caraṇāravindam. So Kṛṣṇa is teaching. Kṛṣṇa is so kind. He's personally teaching, that is, "Perform yajña." He's personally chanting, dancing, Caitanya Mahāprabhu. The picture is in our front. Personally He's teaching us, "Perform this yajña, you rascal, and you'll get everything. You'll get everything." Now, where is the proof? The proof is Kṛṣṇa consciousness movement. We are simply chanting Hare Kṛṣṇa mahā-mantra and spending crores of rupees.
(740928 - Lecture SB 01.08.18 - Mayapur)

Vṛndāvana dāsa Ṭhākura is one of the ācāryas. He has written Caitanya-Bhāgavata. As there is Śrīmad-Bhāgavata, he has written Caitanya-Bhāgavata. Perhaps you have heard the name. So his opinion is, muci haya śuci haya yadi kṛṣṇa bhaje.
Muci and śuci, just opposite. Muci means the most nasty cobbler. He eats everything and does all nonsense. He is called muci. Muci means cobbler. In India, when a cow or bull dies, these muci class are called to take away the carcass. So they take it away and they take out the skin and tan it for . . . this is the original system of shoe-making. And make some shoes and sell in the market. But not by killing cows. When it dies. So this business is done by the muci class. And they take the flesh also. After taking out the skin, the flesh they take. Therefore they are considered very low class, muci. And śuci means brahmin.
So Vṛndāvana dāsa Ṭhākura says, muci haya śuci haya. A cobbler, muci, can become a śuci, yadi kṛṣṇa bhaje, if he's Kṛṣṇa conscious. That's all. If he's Kṛṣṇa conscious, never mind he is a cobbler, he becomes immediately brahmin. Muci haya śuci haya yadi kṛṣṇa bhaje. Śuci haya muci haya yadi kṛṣṇa tyaje. And even if he's born in a brahmin family, if he gives up Kṛṣṇa consciousness, he's immediately cobbler.
(break) So don't lose this opportunity. Always remember Kṛṣṇa, Kṛṣṇa, Kṛṣṇa. (laughter) Don't become cobbler. (break)
(691226 - Lecture Initiation - Boston)