I believe In One Holy, Catholic, and Apostolic Church
The Church is one because it is the Body of Christ: Christ cannot have many bodies. When we say ‘One Church’ we also mean that only in this ‘one’ Church can we find salvation.
The Church is one even though there are many Christians all over the world. Remember the example of Christ the Shepherd — the sheep are many but there is one sheepfold and one Shepherd. The Church isn’t divided into branches with each containing a small part of the Church because each church building and its faithful together are the whole Church.
Our most important duty as Orthodox Christians is to live our lives according to the teachings of the Church because it is only from within the One Church that we have the possibility of living as Christ commanded.
The Church is holy because it is the Body of Christ. Although we are sinners, by being members of Christ’s Body, the Church, we can unite ourselves with Christ. Only within this Holy Church can we partake of the Body and Blood of Christ in the Eucharist.
The word catholic means ‘universal.’ The Church is called catholic both because it is known throughout the world and because it possesses all truth. Only within the Church can we be united with Christ. It is also called catholic because all of us have a common life in Christ in the Church. We are all sinners, but we are all united in faith as members together of the Body of Christ. We all have the possibility to become gods by grace.
The word apostle means ‘someone who is sent.’ The Church is called apostolic because Christ was sent by the Father to unite us with his Body in the Church. Christ is the Father’s Apostle as St. Justin the Martyr writes:
Much has been written to prove that Jesus the Christ is the Son of God and the Father’s Apostle. He is the Word Who existed from before the ages, Who appeared sometimes in the form of fire, and sometimes in the likeness of angels; but now, by the will of God, He has become man for the race of man.
The Church is also called apostolic because it is based on the teaching of the apostles. The Church is still apostolic even now. The Orthodox Church preserves her apostolic succession; the bishops are ordained in a continuous line from the apostles. Just as important as the actual physical connection between our bishops and the apostles is the fact that they hold the same faith as the apostles.
Excerpt from 'The Ark of Salvation'