Before the major Council of Chalcedon all of the original sees established by the apostles where united.
These include Eastern Orthadox and Oriental orthadox.
At this point of Christianity the Nicean-Constantinople creed marked the church with 4 attributes. That being
One, Holy, Catholic and Apostolic.
There is only 1 Church that has these 4 marks and that is the Catholic Church. The Catholic Church is the One holy catholic and Apostolic Church.
One - The Church is one church, it is united both through theology and heirarchy. The eastern orthadox churchs aren’t united through heirarchy OR theology. Although they are all “in communion” with each other, their respective patriarchs often disagree on theological issues and don’t recognise certain eparchy for eg the Greek Orthadox eparchy in the USA. The Easter Orthadox Church is NOT one. Therefor in can’t be the One True Church Established by Christ. The Catholic Church on the other hand is, Patriarchs of the Easter Catholic Churches even if they have their own Canon Laws are still united with Rome through Theology AND hierarchy.
Holy - The Church must be Holy. It MUST respect, make available and uphold the Sacraments as placed by Our Lord Jesus Christ himself. The Catholic Church does this and to be fair so do the Orthadox Churches.
Catholic - The Church must be established by our Lord for the salvation of ALL Souls, it is a universal church for ALL men. Not only the Greek or the Russian or the Coptic ethnicities. Although it is harder to disprove that the Orthadox church is not Catholic. One can only look at history and observe that although the Greek Orthadox initially was richer and had more resources than Rome, it did NOT evangelise the same way the Catholic Church did. The Catholic Church is Universal and continues to evangelise while the Orthadox do not see evangelisation as their mission anymore.
Apostolic - The Church must be headed by a valid Apostle or (Bishop) in modern-day language. Both the Orthadox and the Catholic church have this. However there are only 2 churches that claim the seat of St Peter and that is the Catholic Chuch and the Syriac Orthadox Church. The Syriac Orthadox Church’s claim is invalid has it equals the seat of saint peter to that of St Mark in alexandria (this is fundamentally incorrect) as Christ entrusted his Church to St Peter to be his vicor not a person who is “First among equals”.
Christ build his church on himself as the unshakeable rock that evil can’t triumph over he gave Saint Peter the keys to heaven. It is the Church that St Peter is head of that will be the only way to heaven (as symbolised by the keys), there is no other way to heaven apart from the VISIBLE institution that St Peter himself was made the head of.
[18] And I say to thee: That thou art Peter; and upon this rock I will build my church, and the gates of hell shall not prevail against it. [19] And I will give to thee the keys of the kingdom of heaven. And whatsoever thou shalt bind upon earth, it shall be bound also in heaven: and whatsoever thou shalt loose upon earth, it shall be loosed also in heaven.