Why has marriage to be at Church? When a believer marries a non-believer, how should the relatives of the believer react to such a marriage?
Let's first define marriage. According to the world, marriage is a life long social and legal union between a man and a woman as husband and wife (Although unfortunately even this definition is currently challenged by homosexuals in the courts). In our Coptic Orthodox faith marriage is a Mystery and a Sacrament; and is therefore officiated in the church. It is considered a union between three, man and woman and God. We believe that God unite the two to become one in Him "So then, they are no longer two but one flesh. Therefore what God has joined together, let not man separate" (Mt 19:6). A person who marries an unbeliever chooses, out of their own free will, to separate themselves from the Lord to join in an earthly union with a non believer. "Do not be unequally yoked together with unbelievers. For what fellowship has righteousness with lawlessness? And what communion has light with darkness?" And what accord has Christ with Belial? Or what part has a believer with an unbeliever?" (2 Cor 6:14-15).
Having said that; this Christian person has chosen to be separated from God and loved an unbeliever. Our duty is to talk to this person and try to make them realize the wrong choice they have made; and that they are living in sin rejecting the Lord and committing adultery, since the Church does not recognize this marriage. We should make every effort to correct the situation and get this lost sheep back to church. However, if they are convinced that each one has their own religion and are happy the way they are, we cannot accept them on a social basis and should not befriend them. St. Paul made it clear that it is the church's responsibility to discipline its members. We are not to have fellowship with those who claimed to be Christians; but whose lives were dominated by sin (1 Cor 5:9-13).