Keralites believe that one of Jesus' disciples himself, Didymus Judas Thomas (didymus meaning Twin, but no one knows for sure who his twin brother was , or was it even a Sister who was twin) , so Thomas came to kerala, (known as Thoma in Syriac) and converted Kerala Namboodiris famililes to Christians and other families belonging to lower caste in then society (though everybody like to ignore and eventually forget about the backward caste people who continued to get converted over centuries).
Christianity came to this part of the country (kerala) many centuries ago which is the main reason as to why there are many Christians in Kerala; and also there were many colonies and trade establishments - Portuguese ,French and English, who also brought along missionaries and the fact that kerala remained comparatively poor and extremely casteist region also helped the missionaries in their mission to spread love in the name of Jesus.....