Malayali SyrChr freshmen like me are drawn to the history of Syrian Christians of Kerala (SyrChrs) mainly to find answers to two particular questions:
What sort of Christianity prevailed here originally? That is before the arrival of the Portuguese. Were we originally Orthodox or Catholic?
What does it mean to be a SyrChr?
Lets consider the historical facts and come to a conclusion ... rather a concensus. Many SyrChrs will have difficulty accepting this given the kind of conditioning we have had all through our formative years.
So what was the Malsabha: the sabha (church/community) of Malabar or Malankara?
Was it Syro-Malabar Catholic?
No. The Syro-Malabars were labeled 'Pazhayakoor' (old party) only because they had retained the previously-prevelant Chaldean liturgy, which was then later sadly discontinued. Moreover, there are no proper evidence of "Catholicism" gaining any proper foothold in Kerala prior to the Portuguese.
Was it the Jacobite?
Not either, a large-scale formal association with this sect occurred only after the 1653 coonen cross oath. These associates are labeled 'Puthenkoor' because this section of the Malsabha after the 1653 schism changed their earlier liturgical language from Chaldean (East-Syriac) to West-Syriac.
However most Oriental churches were supposed to be within the larger umbrella of influence under the Patriarch of Antioch, which is hard-core Syrian Orthodox (i.e Jacobite). But the reality was that these churches were left to fend for themselves most of the time.
Was it the Latin Catholic?
Again, since there is little proof of Latin Catholic presence prior to the Portuguese the answer tends to be negative. However there is a record of at least one such station in Kerala since 13th century but little knowledge of the size of the crowd. There just might have been just a handful of Latin Catholics since then.
Was it any of these: Indian Orthodox Church, Syro-Malankara Catholic, Marthoma or the Thozhiyoor sabha?
No, all of these are new splinter groups from the Jacobite stream.
Was it Assyrian or what is otherwise called Nestorian?
Not exactly. Since the Malsabha was a kind-of disillusioned lot they accepted spiritual-leadership from whoever came in 'Syriac' (Middle-Eastern) vestments.
The Assyrian church of the East had managed to seep much into hinterland Asia (India, China etc) prior to the Portuguese. It is suspected that from 5th century most of the Malsabha were Nestorian. One research points out that the Malsabha mass, pre-Portuguese, had some oddities of both Antiochian and Assyrian rituals. Anyways, the Nestorian foothold slipped when the majority of the Malsabha discarded them in the Portuguese finger-points at heresy.
From my gatherings so far, at least from the 3rd century to the coming of the Portuguese, the Malsabha was a bunch of estranged parishes segregated across kingdom lines. It seems it was meant to be part of the Chaldean Orthodoxy and to be governed from Babylon. But since this centre positioned Nestorianism very early, the Malsabha was also infected soon (not in negative sense)
And IF there was a Malsabha before the 3rd century it should have been bunch of neo-Christian groups, led by a community pastor, paralleling the Judeo-Christian groups of early christianity.