Why Orthodoxy is the True Faith (Extended Version)

Antiquity. Universality. And Consensus.

These are the three marks of truth, according to Saint Vincent of Lerins, and -among all Christian denominations- only Orthodoxy possesses all three of them, as we shall easily show in the following paragraphs:

Protestantism lacks all three of them, primarily antiquity, the first Protestant denominations dating back to no sooner than the 16^th century, or -more precisely- to 1517 AD. Even the so-called Pre-Reformers did not exist prior to the 12^th, 14^th, or 15^th centuries.

Among the remaining four¹ ancient and apostolic churches, only Orthodoxy possesses universality, as we shall now demonstrate:

Catholicism is distinguished by its unique, local belief in the Filioque, completely unknown to all other ancient and apostolic churches.

Monophysitism or Miaphysitism is distinguished by its unique, local belief in the one nature of Jesus Christ, completely unknown to all other ancient and apostolic churches.

Nestorianism is distinguished by its unique, local belief in the two persons of Jesus Christ (Jesus the man, and Christ our God), completely unknown to all other ancient and apostolic churches.

	Protestantism	Catholicism	Orthodoxy	Monophysitism	Nestorianism
Antiquity	No	Yes	Yes	Yes	Yes
Filioque	-	Yes	No	No	No
One Nature in Christ	No	No	No	Yes	No
Two Persons in Christ	No	No	No	No	Yes

Therefore –among all the ancient and apostolic churches– Orthodoxy is the only one that possesses catholicity, being thus "the one holy catholic and apostolic church" of the Nicene creed.

¹ I did not take into account artificial hybrids, or unification movements, such as Eastern Catholicism (between Catholicism and Eastern Orthodoxy), Oriental Catholicism (between Catholicism and Oriental Orthodoxy), and Monothelitism or Monoenergism (the Maronites of Lebanon: between Eastern and Oriental Orthodoxy), all of which lack both antiquity, as well as universality.