Below we have a small section from four different lectures by Srila Prabhupada where he takes us through the steps of becoming a real devotee, a Vaishnava. Because it is Kali yuga, many persons who chant Hare Krishna maha mantra take this movement very cheaply and consider themselves a "devotee" whereas in reality we are far from it. Nonetheless, to chant the Holy Names is very good, and we should never stop it, but the qualifications and behavior also must follow along and below we see why.

Prabhupada: And you must see that what you are doing, that is according to the principle which all other sadhus and devotees do. They have tilaka, and you say, "I have no tilaka." That is not sadhu-marganu. Sadhu-marganugamanam. They have kanthi. You say, "I can avoid it." That is not sadhu-marganugamanam. So, from very beginning, if you disobey, then how you'll make progress?
Conversation, January 27, 1977, Bhubaneswar

This is very nice challenge. Suppose if somebody, if you say that "We are Krishna conscious persons." So one may challenge you, "First of all, explain what you know about Krishna?" That is quite natural. If you do not know about Krishna, you have no right to say that "I belong to the Krishna consciousness movement." You have no right to say. So your position is like that, simply if you have a tilaka and a kanthi that does not mean that you belong to the Krishna consciousness movement. Any cheater can do that. You must know the philosophy. If one challenges, you must reply. Therefore Bhaktivinoda Thakura has sung a song indicating these cheaters. He says, ei oto ek kalir cela(?). "Here is a servant of Kali." What kind of cela? Na te tilal golai mala (?). "He has got a tilaka and golai mala, bas, that's all." He does not know what is the philosophy. If you do not know the philosophy of Krishna consciousness, if you simply mark your body with tilaka and kanthi, then you are not proper servant, you are not qualified. So tilaka, mala, is necessary. Just like a policeman. A bogus man, if he dresses like a policeman, he is not a policeman. He must know what is the police law, criminal law, who is to be punished, who is not to be punished, what is criminality, what is innocence. All these things he must know.
Lectures, June 4, 1976, Los Angeles

The guru must be mahatma and muni. Muni means thoughtful, philosopher. Not foolish rascal, manufacturing some philosophy. And mahatmabhih. Not only self-realized, but by his character, by his behavior, by his understanding, he must be a mahatma. What is that mahatma? There are so many mahatmas, simply by changing the dress. No. Not that kind of mahatma. Our Bhaktivinoda Thakura has sung a song, eita eka kalir cela: "Here is a disciple of Kali." What is that? Nake tilaka galai mala. "He has got tilaka..." Nata nara nake tilaka galai mala. He sings that, sahaja bhajana kache namu sange laiya pare dala. (?) Bhaktivinoda Thakura sings that "He's dressed like a babaji. He has shaven his head, and has got tilaka and kanthi. But he has got at least half a dozen women, and that is his bhajana." So not that... That is not mahatma. That is duratma, a cheating... Of course, in this Kali-yuga... Therefore Bhaktivinoda Thakura says, eita eka kalir cela. Kalir cela means the disciple of Kali. Dressed like a sadhu, or Vaishnava, but within, all rubbish things. That will not help us. He must be mahatma, real mahatma. We want guru like that. We must be also qualified, and guru also qualified. Therefore it is said in the Hari-bhakti-vilasa that one year should be taken to study one another, the guru and the disciple. .....
Lectures, August 10, 1974, Vrindavan

So that is called vairagya. Vasudeve bhagavati, vairagya. This is required. Bhaktih paresanubhavo viraktir anyatra syat. Bhakti means when he realizes, God realization, then naturally he becomes unattached to material activities. That is the test. Not that simply by having tilaka or kanthi, one becomes a devotee. How much he is detached to the material attraction. That is the test. Vasudeve bhagavati bhakti-yogah prayojitah janayaty asu vairagyam. If he has no vairagya, if he is still attached to material things, his devotion is not yet...

So these things are very nice. I will request you to study what is bhakti, what is pure devotion, what is Vasudeva. Everything is there. It is a science, great science. It is not sentiment, neither it is so-called religious faith. It is a science. Vijnanam. Yad vijnanam samanvitah. So people do not know. Therefore they take it as a religious movement and reject it. No. Don't reject it. It is a science. You try to understand if you have got brain.
Lectures, November 13, 1973, Delhi