It says first-class, second-class and third-class devotees, they are pure devotees

Expressions researched:
"says first-class, second-class and third-class devotees, they are pure devotees"

Nectar of Devotion Lectures

Yes, pure devotee is anyone who has no other motive except to serve Kṛṣṇa. It doesn't matter he's first class, second class or third... Anyābhilāṣitā-śūnyam. If he has got some motive, then he's not pure devotee. He may be not advanced, but if he has not motive, then he's pure devotee. If he wants to utilize Kṛṣṇa for his personal benefit, then he's not pure devotee. He's impure. So first of all he has to become pure devotee.

The Nectar of Devotion -- Vrndavana, November 4, 1972:

Acyutānanda: ...says first-class, second-class and third-class devotees, they are pure devotees.

Prabhupāda: Yes, pure devotee is anyone who has no other motive except to serve Kṛṣṇa. It doesn't matter he's first class, second class or third... Anyābhilāṣitā-śūnyam (Brs. 1.1.11). If he has got some motive, then he's not pure devotee. He may be not advanced, but if he has not motive, then he's pure devotee. If he wants to utilize Kṛṣṇa for his personal benefit, then he's not pure devotee. He's impure. So first of all he has to become pure devotee. (end)