Why does the Church call marriage a sacrament, and why can it not be dissolved?

Marriage is a sacrament because Paul says the one flesh union of husband and wife corresponds in some mysterious way to the union of Christ and his Church, and it cannot be dissolved because Jesus said what God has joined together let no man put asunder, which means no man, including the two who married. Ephesians 5:31-32 is where this begins. Paul quotes Genesis, for this cause shall a man leave his father and mother and cleave to his wife, and they shall be two in one flesh, and then he says, this is a great mystery, but I speak in Christ and in the Church. The Greek is mysterion, the word the New Testament uses twenty-seven times and which English Bibles always render as mystery. The Vulgate renders it here as sacramentum, and I want to be honest about why. Sacramentum was chosen at this verse because marriage had already been recognized as one of the seven sacraments, and since verse 31 concerns marriage the translation seemed fitting. So the verse does not by itself prove the sacrament, it presupposes it. What the verse does give us is the reason marriage is sacramental. Paul is saying something no one else in Scripture says directly: the relationship of husband and wife in the human realm, including the sexual relationship of the one flesh, corresponds in some mysterious way to our relationship with Christ in the heavenly realm, so that Christ is a spiritual husband and the Church is a spiritual wife. We would not know this mystery if Scripture had not told us, and Paul does not elaborate, because that knowledge only comes at the consummation of all things. But once you see it, the indissolubility follows. Christ does not divorce his Church. A union that signifies that one cannot be an arrangement you exit when it stops suiting you. Trent made it dogma. Canon 1: if anyone says that matrimony is not truly and properly one of the seven sacraments of the evangelical Law, instituted by Christ the Lord, but that it has been invented by men in the Church, and does not confer grace, let him be anathema. Look at the last clause: it confers grace. Not a blessing laid over a natural arrangement, but a channel of actual help for two people who are going to need it. Now the harder half. Jesus is asked in Matthew 19 whether a man may put away his wife for any cause. He goes back behind Moses to the creation: from the beginning he made them male and female, and the two shall be one flesh, therefore now they are not two but one flesh, what God has joined together let no man put asunder. The Greek pronoun there is neuter, which broadens it to anything God joins, and that indicates how strong the divine action between husband and wife really is. When the Pharisees press him on Deuteronomy 24, he answers that Moses permitted it because of the hardness of their hearts, but from the beginning it was not so. The Mosaic permission was a legal accommodation to a sinful people, never God's law. Then comes the exception clause: whoever puts away his wife, except it be for fornication, and shall marry another, commits adultery. This is where Protestants and Catholics split. Protestants apply the exception to the remarriage. Catholics apply it only to the divorce, and that goes back to the Fathers. When one spouse commits fornication, the marriage is already in a state of separation, because that act is the ultimate offense against it. So the innocent spouse does not sin in separating. He may even get that separation recognized by the civil law. But separation is not dissolution. The bond is not broken, because man cannot break what God joined. In the eyes of God and the Church you are still married. So the answer to the question every wounded spouse asks, may I remarry, is no. Two arguments confirm the Catholic reading. First, position. If the exception applied to the remarriage as well as the divorce, we would expect it at the end of the sentence where it would cover both clauses, not stuck in the middle. Second, the companion verse. Matthew 5:32 says that whoever divorces his wife, except for fornication, causes her to commit adultery, and whoever marries her commits adultery. The divorcing husband is held responsible for two adulteries, hers and her new husband's, and that only makes sense if her second marriage is adulterous, which it can only be if she is still bound to the first man. Augustine saw it clearly: a spouse is lawfully dismissed for cause of fornication, but the bond of chastity remains, which is why a man commits adultery if he marries a woman dismissed even for that reason. And again: the sacramental bond, which they lose neither through separation nor through adultery, this the spouses should guard chastely and harmoniously. Trent Canon 7 condemns anyone who says the Church errs in teaching that the bond cannot be dissolved for adultery and that neither party, not even the innocent one, may remarry while the other lives. Canon 8 protects the other side: the Church does not err in permitting separation from bed and board for many reasons. Two real exceptions exist and neither breaks a sacramental bond. A ratified but unconsummated marriage can be dissolved by solemn religious profession, which is Trent Canon 6. And the Pauline privilege of 1 Corinthians 7:15 applies where two unbaptized people married, since that marriage is true but not ratified. Even there, if the unbelieving spouse is willing to stay, you are obliged to stay. It is not a door out of marriage.