Were the ancestors of Christians and Muslims in India Hindus at some point?

I am a St.Thomas Christian, Kerala

CHRISTIANITY OLDER THAN HINDUISM IN KERALA

From my understanding the word Hindu and Hinduism are quite modern terms and it was ‘Sanadhana Dharma’ that existed in Indian sub-continent. Most of the converts were indigenous people, but whether they all followed ‘Sanadhana Dharma’ is uncertain.

St. Thomas Christians, also called St. Thomas Christians or Malabar Christians, indigenous Indian Christian groups who have traditionally lived in Kerala, a state on the southwestern or Malabar Coast of India. Claiming to have been evangelized by St. Thomas the Apostle, Thomas Christians ecclesiastically, liturgically, and linguistically represent one of the oldest Christian traditions in the world, particularly in Christianity outside the West.

Although no longer a single institutional Church, Thomas Christians altogether constitute a vibrant religious community. In the early 21st century there were about four million Thomas Christians in India, mainly within Kerala, and a small worldwide diaspora.

At that time Jainism was prominent in Kerala; the Jews in Kerala also converted to Christianity . In the past 2000 years through marriage these different lineages got mixed up.

Hence to say the ancestor was Hindu or he was not Hindu is does not make any sense.

Talk:Syrian Malabar Nasrani

Where do Syrian Christians come from? DNA testing provides some interesting answers. - KochiPost

The myth of pure breed is flowed, people those converted were Jain, Jew, probably Hindu. Over the centuries they have all mixed(married) and formed the present day St.Thomas Christian

• Knanaya/ Tekkumbhagar (Early Christian migrants)

Knanaya are an endogamous(marry within) group within Saint Thomas Christians. They look(features) quite different from rest of the Saint Thomas Christians, have unique customs, their cuisine is also different.

They are said to be descendants of Thomas of Cana(Kinai-Thoma), a Syrian merchant who led a group of 72 immigrant families from the Middle East to settle in India in the 4th century (some sources place these events in the 8th century).

During to splits among St.Thomas Christians today the majority of Knanaya are members of the either Syro-Malabar Catholic Church or Malankara Orthodox Syrian Church or Syro-Malankara Catholic Church. Can find few among Jackobles and in Marthoma Churches as well. Few have joined Pentecost churches.

DNA test confirm their middle east connection

The Syro-Malabar Catholic Archeparchy of Kottayam is specially for Knanaya Catholics(in Syro Malabar).

What do you know about "knanaya" community?

[Jainism

Jainism is considered to have reached Kerala in 3rd century BC. Chandragupta Maurya left his throne in the 25th year of his reign and reached Mysore with a Jain monk named Bhadrabahu. The disciples of Bhadrabahu went in

search of a tranquil place for meditation throughout South India and spread the religious ideas. Thus Jainism spread into Kerala as well.

Buddhism

The number of Buddhists is less than Jainists in Kerala. Like Jainism, Buddhism is also believed to have entered Kerala in and around 3rd century BC, during the reign of Ashoka. Many old Tamil poems like Ettuthokai and Pathuppattu have mentions of Buddhist monks' works to propagate the ideals of Buddha. The famous poem Manimekhalai is a poem with ideals of Buddhism. A number of Buddha idols have been recovered from Karunagappally, Kunnathur and Ambalappuzha, Aala and Paruvassery. The most important Buddhist temple in Kerala was Sreemoolavasam.]