I am trying to develop a “St Thomas Proof” for Catholic Christianity. This is the premise:
The Apostle Thomas established the church in India that survives to this day (and is now in communion with the Catholic Church). Since St Thomas established a church in India, which was far away from the Holy Land and Rome, and the current India church is clearly Catholic, this provides proof that the Catholic Church contains the fullness of truth passed on from the apostles.
Some question whether Thomas himself actually evangelized India; and it is a question that is open to debate?
Some claim that he did not leave them with one written word of New Testament Scripture?
Some claim there’s no reasonable basis to claim that Thomas didn’t bring any New Testament Scripture with him?
Some claim the Indian Orthodox church (also known as the Malankara Orthodox Syrian Church) uses the so-called Liturgy of St. James. That liturgy includes the reading of the gospels?
Some claim the Malankara church was out of communion with Rome for centuries (whether it is now in full communion is an interesting question in itself). Isn’t it odd to point to a church that was apart from communion with Rome as though it were an example of authentic Christianity?
Did St. Paul have more authority to pass on the faith than St. Thomas?
Please provide additional arguments to support this proof and provide counter arguments for claims against the proof.