In this verse the words daya jivesu, meaning "mercy to other living entities," indicate that a living entity must be merciful to other living entities if he wishes to make progress in self-realization. This means he must preach this knowledge after perfecting himself and understanding his own position as an eternal servant of Krsna. Preaching this is showing real mercy to living entities. Other types of humanitarian work may be temporarily beneficial for the body, but because a living entity is spirit soul, ultimately one can show him real mercy only by revealing knowledge of his spiritual existence. As Caitanya Mahaprabhu says, jivera 'svarupa' haya-krsnera 'nitya-dasa': [Cc. Madhya 20.108] "Every living entity is constitutionally a servant of Krsna." One should know this fact perfectly and should preach it to the mass of people. If one realizes that he is an eternal servant of Krsna but does not preach it, his realization is imperfect.

From Srila Prabhupada's purport to SB 4.29.1b