An Orthodox Christian holds the beliefs of the Orthodox Catholic Faith, which was held and taught by the Holy Apostles. It is summarized in the Symbol of Faith, sometimes called the Nicene Creed:
The essential beliefs of the Orthodox Christian are therefore very much the essential beliefs of all Christians–the existence of God as Holy Trinity; the Incarnation of the Son as the God-Man Christ Jesus; and His passion, death, and resurrection. Beyond the beliefs stipulated in the Creed, an Orthodox Christian believes in all the doctrines of the Seven Ecumenical Councils, held between AD 325 and AD 787.
Orthodox Christians, however, hold that these beliefs are part of an entire way of believing, living, and worshipping that comes to us from the Apostles. This we call “Holy Tradition.” Our liturgical worship, our use of the Holy Icons, our prayers for the departed, our veneration of the Saints, and especially of the Mother of God–all of these are part of Holy Tradition. For the Orthodox, it is not possible to accept some parts of this and reject others; these beliefs and practices make up an organic whole, which is nothing more or less than Christianity itself.
4th Stasis of the Salutations to Theotokos – Saint Nicholas’ Church, Cardiff – 16/3/2018 Δ’ Χαιρετισμοί στην Υπεραγία..