Three truths for a preacher

Prahlāda Mahārāja ultimately instructed his class friends, the sons of the demons, to accept the process of devotional service by preaching the science of Kṛṣṇa consciousness to everyone. Preaching is the best service to the Lord. The Lord will immediately be extremely satisfied with one who engages in this service of preaching Kṛṣṇa consciousness. This is confirmed by the Lord Himself in Bhagavad-gītā (18.69). Na ca tasmān manuṣyeṣu kaścin me priya-kṛttamaḥ: "There is no servant in this world more dear to Me than he, nor will there ever be one more dear." If one sincerely tries his best to spread Kṛṣṇa consciousness by preaching the glories of the Lord and His supremacy, even if he is imperfectly educated, he becomes the dearmost servant of the Supreme Personality of Godhead. This is bhakti. As one performs this service for humanity, without discrimination between friends and enemies, the Lord becomes satisfied, and the mission of one's life is fulfilled. Śrī Caitanya Mahāprabhu therefore advised everyone to become a guru-devotee and preach Kṛṣṇa consciousness (yāre dekha, tāre kaha 'kṛṣṇa'-upadeśa [Cc. Madhya 7.128]). That is the easiest way to realize the Supreme Personality of Godhead. By such preaching, the preacher becomes satisfied, and those to whom he preaches are also satisfied. This is the process of bringing peace and tranquillity to the entire world.

bhoktāraḿ yajña-tapasāḿ

sarva-loka-maheśvaram

suhṛdaḿ sarva-bhūtānāḿ

jñātvā māḿ śāntim ṛcchati

[Bg. 5.29]

One is expected to understand these three formulas of knowledge concerning the Supreme Lord — that He is the supreme enjoyer, that He is the proprietor of everything, and that He is the best well-wisher and friend of everyone. A preacher should personally understand these truths and preach them to everyone.

Srimad Bhagvatam, Srila Prabhupada purport to 7.6.24