Sri Bhagavan uvaca:

“Pure devotees are those who thoroughly understand the Supreme Personality, become fully engaged in My service and talk about Me and preach about Me, and thus they are satisfied and enjoy spiritual bliss. “

So this is a pure-devotee-meter. Just like there are altimeters to determine altitude, there are barometers to determine atmospheric pressure and there are tyres pressure meters to inflate, deflate and check tyre pressure, similarly here we have a pure-devotee-meter supplied courtesy Sri Bhagavan, through the intermediary of His ten thousand years appointee Srila Prabhupada. Please take the test.

There are five parameters here:

1. The degree of development of one’s knowledge of God, Krishna, through Prabhupada Shastra.
2. Full engagement in Krishna’s service or in other words, degree of one’s engagement in Krishna’s service under proper authority.
3. Talk about Krishna, perhaps with fellow devotees, etc, exchange of realization about Krishna, etc, i.e. sadhu sanga.
4. Preaching to the mass of people. There are two things to be mentioned here.

Caitanya Caritamrta, Madhya Lila, Chapter 7, TEXT 101

yare dekhe, tare kahe, — kaha krsna-nama
ei-mata ‘vaisnava’ kaila saba nija-grama

SYNONYMS
yare dekhe — whomever he meets; tare — to him; kahe — he says; kaha krsna-nama — kindly chant the Hare Krsna mantra; ei-mata — in this way; vaisnava — devotees of the Supreme Personality of Godhead; kaila — made; saba — all; nija-grama — his own village.

TRANSLATION
Such an empowered person would request everyone and anyone — whomever he saw — to chant the holy name of Krsna. In this way all the villagers would also become devotees of the Supreme Personality of Godhead.

PURPORT
In order to become an empowered preacher, one must be favored by Lord Sri Caitanya Mahaprabhu or His devotee, the spiritual master. One must also request everyone to chant the maha-mantra. In this way, such a person can convert others to Vaisnavism, showing them how to become pure devotees of the Supreme Personality of Godhead.

Here one is advised to actually take the trouble and time to run people we meet through the full Hare Krishna maha-mantra at least once, word after word. It means the devotee speaks one word “Hare” and the interlocutor repeats “Hare”. Then next word “Krishna”, next word again “Hare” etc, etc, through all sixteen words. I have just met again an intelligent lady who chanted with me like that 4 or 5 years ago in Jennifer st in front of the Brisbane ISKCON temple. I did not recognize her and when I ask her to chant again the maha-mantra she told me the story. Now she is becoming more advanced and is reading the Bhagavad-gita As It Is.

The other thing is Srila Prabhupada eternal statements about the importance of book distribution:

Calcutta
21 February, 1972
72-02-21

San Diego
My dear Bhakta das,
Please accept my blessings. I beg to acknowledge receipt of your letter of January 28, 1972, and I am pleased to note that everything is progressing nicely in San Diego center. I especially appreciate your attitude toward increasing more and more the sales of our books, that will sanctify all other activities of preaching because preaching means selling books.
……………………………………………………..
I Hope this will meet you in good health and happy mood.
Your ever well-wisher,
A.C. Bhaktivedanta Swami
ACBS/sda

AND

Bombay
10 January, 1972
72-01-10

East Cleveland
My dear Sri Govinda,
Please accept my blessings.

…………. I am pleased that your distribution of literatures is also increasing. Go on giving this matter your full attention. The more books we sell, the more we ourselves advance in Krishna Consciousness.
Regarding your proposal to open one store, that is not a very good proposal. Our devotees cannot work in that way. Better they are preaching and selling books door-to-door.

I hope this will meet you in good health and cheerful mood.
Your ever well-wisher,
A.C. Bhaktivedanta Swami
ACBS/sda

and 5 ) How happy and satisfied am I from my engagement in the service of Krishna, the Supreme Personality of Godhead. Am I actually enjoying spiritual bliss?