Yet man professes to belong to a particular type of faith with reference to a particular time and circumstance and thus claims to be a Hindu, Muslim, Christian, Buddhist or an adherent of any other sect. Such designations are non-sanātana-dharma. A Hindu may change his faith to become a Muslim, or a Muslim may change his faith to become a Hindu, or a Christian may change his faith and so on. But in all circumstances the change of religious faith does not affect the eternal occupation of rendering service to others. The Hindu, Muslim or Christian in all circumstances is servant of someone. Thus, to profess a particular type of faith is not to profess one's sanātana-dharma. The rendering of service is sanātana-dharma.
Factually we are related to the Supreme Lord in service. The Supreme Lord is the supreme enjoyer, and we living entities are His servitors. We are created for His enjoyment, and if we participate in that eternal enjoyment with the Supreme Personality of Godhead, we become happy. We cannot become happy otherwise. It is not possible to be happy independently, just as no one part of the body can be happy without cooperating with the stomach. It is not possible for the living entity to be happy without rendering transcendental loving service unto the Supreme Lord.