According to Christ, in order for the love of a man and woman to be that which God has perfectly created it to be, it must be unique, indestructible, unending and divine. The Lord himself has not only given this teaching, but he also gives the power to fulfill it in the sacrament of Christian marriage in the Church.
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.
A specific rite of marriage appeared as early as the 4th century, but it wasn't until the 14th century that the sacramental rite of Holy Matrimony was formalized with a blessing, and the marital union sealed during the liturgy in joint communion with the Holy Eucharist. 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.
According to the Orthodox teaching, only one marriage can contain the perfect meaning and significance which Christ has given to this reality. Thus, the Orthodox Christian tradition encourages widows and widowers to remain faithful to their spouses who are dead to this world but alive in Christ. The Orthodox tradition also, by the same principle, considers temporary "living together," casual sexual relations, sexual relations with many different people, sexual relations between members of thie same sex, and the breakdown of marriages in separation and divorce, all as contrary to the human perfection revealed by God in Christ. Through penance, however, and with the sincere confession of sins and the genuine promise of a good life together, the Orthodox Church does have a service of second marriage for those who have not been able to fulfill the ideal conditions of marriage as taught by Christ. It is the practice of the Church as well not to exclude members of second marriages from the sacrament of holy communion if they desire sincerely to be in eucharistic fellowship with God, and if they fulfill all other conditions for participation in the life of the Church.
Because of the realization of the need for Christ in every aspect of human life, and because, as well, it is the firm Christian conviction that nothing should, or even can, be done perfectly without Christ or without his presence and power in the Church by the Holy Spirit, two Christians cannot begin to live together and to share each other's life in total unity: spiritually, physically, intellectually, socially, economically without first placing that unity into the eternity of the Kingdom of God through the sacrament of marriage in the Church.
According to the Orthodox teaching as expressed in the sacramental rite of marriage, the creation of children, and the care and love for them within the context of the family, is the normal fulfillment of the love of a man and woman in Christ. In this way, marriage is the human expression of the creative and caring love of God, the perfect Love of the Three Persons of the Holy Trinity which overflows in the creation and care for the world. This conviction that human love, imitative of divine love, should overflow itself in the creation and care for others does not mean that the procreation of children is in itself the sole purpose of marriage and the unique and exclusive justification and legitimization of its existence. Neither does it mean that a childless couple cannot live a truly Christian life together. It does mean, however, that the conscious choice by a married couple not to have a family for reasons of personal comfort and accommodation, the desire for luxury and freedom, the fear of responsibility, the refusal of sharing material possessions, the hatred of children, etc., is not Christian, and can in no way be considered as consonant with the biblical, moral and sacramental teachings and experience of the Orthodox Church about the meaning of life, love and marriage.
In light of the perspective offered above, the control of the conception of children in marriage is a very delicate matter, discouraged in principle and considered as perhaps possible only with the most careful examination of conscience, prayer and pastoral guidance. The abortion of a child already conceived is strictly forbidden in the Orthodox Church, and cannot be justified in any way, except perhaps with the greatest moral risk and with the most serious penitence in the most extreme cases such as that of irreparable damage to the mother or her probable death in the act of childbirth. In such extreme situations, the mother alone must take upon herself the decision, and all must be prepared to stand before God for the action, asking his divine mercy.