In his response to the joint Catholic-Orthodox declaration, Metropolitan Philaret of the ROCOR states that union with Rome is only possible if "they accept the Orthodox Faith as it is maintained until now in the Holy, Catholic, and Apostolic Church." [1] Absent from that final phrase is mention of the Mark of Oneness or Unity, which, of course, is a thing accepted by the Eastern Orthodox churches as they hold to the Nicene Creed (the 4 being mentioned, in addition to *Orthodox*, by Fr. Seraphim Cardoza here ) which states: > [We Believe in] **one** **holy**, **catholic**, and **apostolic** Church [3] Of the Mark of Unity, the *Catholic Encyclopedia* says that: > The marks of the Church are certain unmistakeable signs, or distinctive characteristics which render the Church easily recognizable to all, and clearly distinguish it from every other religious society, especially from those which claim to be Christian in doctrine and origin. > [the Church which has Christ for its founder] must unite its members in unity of doctrine[...] in unity of worship[...] and in unity of government. [4] That's the Catholic Encyclopedia, though. I'm looking for Orthodox sources. The Wikipedia article doesn't really talk about the Orthodox perspective. The OrthodoxWiki does not have an article on either the Four Marks, or of Unity as a Mark. Is my phrasing the problem? Should I be using different words? What are some sources from Eastern Orthodoxy about the 4 Marks and/or specifically about the Mark of Unity. As of **08-Mar-2022** I found that there is [this article][https://orthodoxwiki.org/Primacy_and_Unity_in_Orthodox_Ecclesiology] on OrthodoxWiki that has a couple sources to use. Namely Metropolitan John Zizioulas, Fr. John Meyendorff, Fr. Alexander Schmemann, and Fr. Thomas FitzGerald. But it seems I'll need to simply read their works for a non-wiki answer.

In the Catholic Church, the "Marks of the Church" are what's in the Nicene creed. That she is one, holy, catholic and apostolic. I've seen that the [Westminster Catechism has different marks](https://christianity.stackexchange.com/questions/7309/origin-of-the-marks-of-the-true-church) spelled out. What does every Major branch of Christianity whose has "Marks of the Church" claim those marks to be? This is a [tag:crestomathy-request], so every answerer who attempts to answer this question should include, within reason, every mark of every church.

In Reformed Theology, "the marks of a true church" are often delineated, to the effect of: 1. Church discipline 2. Teaching/preaching 3. Administration of the sacraments (These are the marks often denoted in systematic theology, but let it be noted that they are not intended to exclude other important marks such as suffering and love.) A slightly altered formula is seen in Westminster Confession of Faith, Chapter 25 *Of the Church*, paragraph 4: > This catholic Church hath been sometimes more, sometimes less visible. And particular Churches, which are members thereof, are more or less pure, according as the doctrine of the gospel is taught and embraced, ordinances administered, and public worship performed more or less purely in them. I found something similar in Calvin's letter to Cardinal Sadoleto (available in Vol. III of Banner of Truth's *Tracts and Letters* Calvin volumes, and in a slim booklet edited by John Olin entitled *A Reformation Debate*, page 63): > Since there are three things on which the safety of the Church is fonded, viz., doctrine, discipline, and the sacraments, and to these a fourth is added, viz., ceremonies, by which to exercise the people in offices of piety... Calvin's letter of 1539 predates the Confession by a little over a hundred years, and is the earliest document that I have personally found this doctrine in. However, I find it unlikely that Calvin wrote any new doctrines in his letter to the Cardinal, so I'm wondering where the origin of this doctrine was. Does Calvin have earlier writings on it? Did earlier Reformers such as Luther, Zwingli or Bucer discuss it? Were there pre-Reformation theologians who discussed it?

Although this very related question about the [marks of the true church](https://christianity.stackexchange.com/questions/7309/origin-of-the-marks-of-the-true-church) in Reformed Theology has already been asked, my question is whether other Protestant traditions or Catholicism have an equivalent set of requirements for what they consider the true church?