Excerpt from "The Orthodox Faith" by Protopresbyter Thomas Hopko:
In the sacrament of marriage, a man and a woman are given the possibility to become one spirit and one flesh in a way which no human love can provide by itself. In Christian marriage the Holy Spirit is given so that what is begun on earth does not “part in death” but is fulfilled and continues most perfectly in the Kingdom of God.
For centuries there was no particular ritual for marriage in the Church. The two Christians expressed their mutual love in the Church and received the blessing of God upon their union which was sealed in the holy eucharist of Christ. Through the Church’s formal recognition of the couple’s unity, and its incorporation into the Body of Christ, the marriage became Christian; that is, it became the created image of the divine love of God which is eternal, unique, indivisible and unending.
When a special ritual was developed in the Church for the sacrament of marriage, it was patterned after the sacrament of baptism-chrismation. The couple is addressed in a way similar to that of the individual in baptism. They confess their faith and their love of God. They are led into the Church in procession.
They are prayed over and blessed. They listen to God’s Word. They are crowned with the crowns of God’s glory to be his children and witnesses (martyrs) in this world, and heirs of the everlasting life of his Kingdom. They fulfill their marriage, as all sacraments are fulfilled, by their reception together of holy communion in the Church.
There is no “legalism” in the Orthodox sacrament of marriage. It is not a juridical contract. It contains no vows or oaths. It is, in essence, the “baptizing and confirming” of human love in God by Christ in the Holy Spirit. It is the deification of human love in the divine perfection and unity of the eternal Kingdom of God as revealed and given to man in the Church.
The Christian sacrament of marriage is obviously available only to those who belong to the Church; that is, only for baptized communicants. This remains the strict teaching and practice of the Orthodox Church today. Because of the tragedy of Christian disunity, however, an Orthodox may be married in the Church with a baptized non-Orthodox Christian on the condition that both members of the marriage sincerely work and pray for their full unity in Christ, without any coercion or forceful domination by either one over the other. An Orthodox Christian who enters the married state with a non-Orthodox Christian must have the sacramental prayers and blessings of the Church in order to remain a member of the Orthodox Church and a participant in the sacrament of holy communion.