"Whatever you may be, either you are poor man or rich man or black man or white man or woman or man, it doesn't matter. Everyone has right to serve Kṛṣṇa. Apratihatā.
There is nothing in the material world which can check one's devotional service. It is so pure and exalted. Ahaituky apratihatā. And if you be situated in such kind of devotional service, yayātmā suprasīdati—immediately you become happy.
That is the standard of happiness. We are seeking, 'I may be happy in this way, I may be happy in that way.' No. You can simply become happy when you are a pure devotee of the Lord, without any reason. Pure devotee. Ahaituky apratihatā yayātmā suprasīdati."
(Srila Prabhupada Lecture, London, August 27, 1971)