Kerala is a strip of coast behind the Western Ghats, and almost everything unusual about its religious composition follows from the fact that it was easier to reach by sea than by land. Roman, Arab, Persian and Chinese traders came for pepper and cardamom, and traditions came with them earlier than they reached most of the interior.
The Saint Thomas Christians trace their church to the apostle Thomas, held to have landed on the coast in the first century. The historical claim is debated and the antiquity of the community is not: there were organised Christians on this coast using Syriac in worship long before European contact, in communion with the Church of the East rather than with Rome, and the attempt by the Portuguese to bring them under Latin authority in the sixteenth century split the community into branches that persist today. Jewish settlement at Kodungallur and later Kochi is similarly old and has now almost entirely emigrated to Israel. Islam arrived by the same route, through Arab trading families, giving the Mappila community a history distinct from the Islam of northern India.
Hindu practice in Kerala is likewise its own. Temple ritual follows Tantric manuals rather than the northern pattern, matrilineal inheritance shaped several communities, and the pilgrimage to Sabarimala draws millions each season along a route that requires weeks of preparatory austerity.