Kṛṣṇa-kathā is the only remedy for all people of the world because it can situate one in pure consciousness of the self and liberate one from material bondage. To preach kṛṣṇa-kathā all over the world, as recommended by Lord Caitanya, is the greatest missionary activity, and all sensible men and women of the world may join in this great movement started by Lord Caitanya.
-Shrimad Bhagvatam Canto 3 Chapter 5 Verse 11, Translation and Purport

नासतो विद्यते भावो नाभावो विद्यते सतः ।
उभयोरपि दृष्टोऽन्तस्त्वनयोस्तत्त्वदर्शिभिः ॥ १६ ॥
Those who are seers of the truth have concluded that of the nonexistent [the material body] there is no endurance and of the eternal [the soul] there is no change. This they have concluded by studying the nature of both.
-BG 2.16