There are different kinds of welfare activities in this material world, but the supreme welfare activity is the spreading of Kṛṣṇa consciousness. Other welfare activities cannot be effective, for the laws of nature and the results of karma cannot be checked. It is by destiny, or the laws of karma, that one must suffer or enjoy. For instance, if one is given a court order, he must accept it, whether it brings suffering or profit. Similarly, everyone is under obligations to karma and it reactions. No one can change this. Therefore the śāstra says:
tasyaiva hetoḥ prayateta kovido
na labhyate yad bhramatām upary adhaḥ
One should endeavor for that which is never obtained by wandering up and down the universe as a result of the reactions of karma. What is that? One should endeavor to become Kṛṣṇa conscious. If one tries to spread Kṛṣṇa consciousness all over the world, he should be understood to be performing the best welfare activity. The Lord is automatically very pleased with him. If the Lord is pleased with him, what is left for him to achieve? If one has been recognized by the Lord, even if he does not ask the Lord for anything, the Lord, who is within everyone, supplies him whatever he wants.
- Śrīla Prabhupāda, Śrīmad-Bhāgavatam 8.7.44 Purport