Missionary activities.

By the mercy of Srila Prabhupada, understand and accept here what this is the basic principle of missionary activities.
SB 2.5.9

brahmovāca
samyak kāruṇikasyedaṁ
 vatsa te vicikitsitam
yad ahaṁ coditaḥ saumya
 bhagavad-vīrya-darśane
Word for word:
brahmā uvāca — Lord Brahmā said; samyak — perfectly; kāruṇikasya — of you, who are very kind; idam — this; vatsa — my dear boy; te — your; vicikitsitam — inquisitiveness; yat — by which; aham — myself; coditaḥ — inspired; saumya — O gentle one; bhagavat — of the Personality of Godhead; vīrya — prowess; darśane — in the matter of.
Translation:
Lord Brahmā said: My dear boy Nārada, being merciful to all (including me) you have asked all these questions because I have been inspired to see into the prowess of the Almighty Personality of Godhead.
Purport:
Brahmājī, being so questioned by Nāradajī, congratulated him, for it is usual for the devotees to become very enthusiastic whenever they are questioned concerning the Almighty Personality of Godhead. That is the sign of a pure devotee of the Lord. Such discourses on the transcendental activities of the Lord purify the atmosphere in which such discussions are held, and the devotees thus become enlivened while answering such questions. It is purifying both for the questioners and for one who answers the questions. The pure devotees are not only satisfied by knowing everything about the Lord, but are also eager to broadcast the information to others, for they want to see that the glories of the Lord are known to everyone. Thus the devotee feels satisfied when such an opportunity is offered to him. This is the basic principle of missionary activities.