The Portuguese created everywhere, even in Rome, the false impression that they had converted the Thomas Christians from the Nestorian heresy and schism. It should be noted that there is a contradiction between this notion and the fact that the Thomas Christians were summoned to the Synod of Diamper under the pain of "excommunication"! (For more details, see Western Influence on Thomas Christians). If the Thomas Christians were not Catholics, why should the Portuguese archbishop (Catholic) excommunicate them?
Since the Thomas Christians of Malabar were ruled by the Chaldean Church (which is said to have received Nestorianism in the 5th century) from 7th century until 16th century, many people suspect Nestorianism in the Malabar Church. From what many eminent historians say, we can conclude that probably they were influenced by the heresy, but because of the type of relationship they had with the Chaldean Church, they were not in schism, and that their Catholic orthodoxy is recognized by most in recent times. The Thomas Christians were legally under the Prelates who were sent by the Patriarchs of the line of Sulaqa who had Roman confirmation. The Patriarch condemned in the synod of Diamper was Denha Simon who was in explicit communion with Rome being also honored with the sacred Pallium from the Pope. Words of Dionisio S.J. is noteworthy: "About the Pope, they consider him as the Vicar of Christ, our Redeemer on earth; (they consider) the Patriarch as subject to the Pope from whom he receives his power."
Pope Julius III ( 1553 ) recognized the jurisdiction of Chaldean Patriarch Sulaqa over all localities and monasteries in Calicuth and in All India. The Chaldean Patriarch Abdiso at the order of the Pope Pius IV assigned the see of Angamaly to Mar Abraham in 1567.
On Jan. 3, 1578, Mar Abraham, bishop of Thomas Christians, wrote to the Pope entreating the latter to protect him from the ill-treatment of the Portuguese. He invited the Jesuits to work under him. The Jesuits preached in churches and heard confessions there. The archdeacon of Mar Abraham, George (of Christ) was confirmed by the Pope as Administrator of Angamaly in the case of vacancy in the see. In 1583 Mar Abraham held a synod at Angamaly with the help of the Jesuits, corrected books, forbade priests to marry, etc. A new seminary was started at Vaipicotta (Chenotta) and entrusted to the Jesuits. Mar Abraham allowed the Jesuits to Latinise his subjects to a certain extent provided the East Syriac language was retained in liturgical functions, but he repented of this. It also should be noted that Mar Jacob, the prelate of the Thomas Christians, was the chaplain of the Portuguese in Cranganore from the beginning, and he said Mass for them in Latin and also heard their confessions.
Even if we accept that the Chaldean Church was Nestorian, it doesn't apply to the Malabar Church, because of the type of relation they maintained. It was found in a letter sent by Archbishop Leo Kierkels, the Apostolic Delegate and the first Internuncio in India (1931-1952) to Father Placid Podipara, a historian of Syro-Malabar Church: " It is plausible to suppose that it (the Indian Church of the Thomas Christians) gradually established communication with the Near East and soon began to introduce books and borrow rites and later prelates and receive immigrants thus the Malabar Church was not a branch or offshoot of the East Syrian one, as was early Christianity in China, but it became and long remained a voluntary associate member of the Syro-Chaldean Patriarchate for practical, not for doctrinal reasons. Their mutual relations were the outcome not of organic development of one moral body, but of historical intercourse between two moral bodies, each retaining separate, corporate responsibility."
The Thomas Christians commonly believed in all the articles of the Nicene Creed and considered their Patriarch as subject to the Pope. About the Catholic orthodoxy of the Syro-Malabar Church, Pope John Paul II said recently: " It is to the glory of this Church that it has not ever been severed from the communion with the Church of Rome, in a continuity that the enormous geographic distance has never been able to break."
Roz S.J., in his thesis 1586/7, says that the Thomas Christians professed the Catholic Roman faith although their books contained Nestorian errors, that they were publicly preaching the Blessed Virgin Mary to be the Mother of God, that they left out the names of Nestorius and others, while they recited or sang the Divine Office. The faith and communion of the Thomas Christians are testified by Carneiro, Ferdinand Paz, Nunes Baretto, Dionisio and Roz.