
The West Syrian bishops present among the Orthodox Thomas Christians from 1665 gradually introduced their church traditions. Exploiting the strong opposition to Roman Catholicism, they introduced doctrinal, liturgical and disciplinary measures. Mar Gregorios (1665) began this work; those who came after him continued it. From the middle of the 19th century the West Syrianization process speeded up. Substantial affinities in language, traditions and discipline between East and West Syrian traditions made the introduction of West Syrian traditions among the Orthodox of India easier.
When accepting the services of Mar Gregorios, the Orthodox of Malabar did not place themselves under the jurisdictional setup of the Antiochene Syrian Church. The West Syrian Patriarch, however, from the beginning desired that the Indian church formally accept him as Supreme Head—similar to the Portuguese extracting submission to Rome in 1599. Mar Thoma V and VI foiled attempts to realize this claim; a party favourable to the Patriarch had formed by the middle of the 18th century and troubled the Mar Thoma bishops. This party was very active during the CMS collaboration (1816–1836) and was a major factor in its collapse.
Between 1709 and 1731 a bishop named Mar Gabriel from the East Syrian Patriarch arrived in Kerala to reclaim the flocks lost since 1599. A number of churches and a considerable body of Thomas Christians, both non-Romo and Romo, accepted him. He died at Kottayam and was buried at Cheriapally. This shows that during the 18th and 19th centuries, until the Orthodox were fully identified with the West Syrian Church, they also remained ecclesiastically identified with East Syrian Christianity. Eastern Syriac remained their liturgical language until Western Syriac was imposed from 1876 after the Synod of Mulanthuruthy. Mar Thoma IV and V clashed with Mar Gabriel both theologically and administratively; Mar Gabriel died without a successor, and with this event the connection of the Indian church with the East Syrian church came to an end. The Portuguese condemnation of the East Syrian Church as Nestorian, and the West Syrian contact’s denunciation of East Syrian Christianity as heretical, gradually led the Indian Orthodox to quit their East Syrian identity and embrace West Syrian identity.