Matrimony (marriage) is unique among the sacraments in that it existed before Christ elevated it into a sacrament. Christ instituted the other six sacraments from scratch, so to speak. In marriage, He elevated an existing institution to the grace of a sacrament, so that husband and wife remain united receive special grace to help each other and their children get to Heaven.
The Sacrament of Marriage is an indissoluble union between one man and one woman, where “a man leaves his father and his mother and cleaves to his wife, and they become one flesh” (Gen 2:24). The spouses are united in a sacramental bond which aids and strengthens their natural union. Marriage is a natural union, and everyone is naturally inclined to it, but Christians must receive the Sacrament of Marriage (being married in the Church) in order to be validly married in the eyes of the Church. However, even natural (unsacramental) marriages are recognized by the Church as real marriages, but Christians who do do not receive the grace of the sacrament of matrimony commit grave sin because they refuse God’s Grace and enter into an intimate union without the Church’s approval.
Contrary to popular belief, everyone is called to chastity, not just the celibate and virgins. For unmarried persons (including dating couples), chastity equates with celibacy. However, because married persons must engage in the conjugal act in order to procreate children, chastity in their case means something a bit different. Of course, husband and wife can only have sex with each other. Moreover, they must always do so for the primary purpose of the sexual act, or at least being “open” to it. This means that they must always engage in the conjugal act with the intention of procreation (the primary purpose of the sexual act), or at least be open to it (no usage of artificial contraception). The natural law, an extra-religious ordering of the universe, indicates that things in nature must be used according to their intended end. For example, it becomes a man to eat food so that he can live and do thrive. Eating something inedible would not contribute to this end, or would even be detrimental to it, and so is impermissible according to natural law. Engaging in the sexual act without being open to the conception of life denigrates the sexual act and turn the focus of it inward, on the couple themselves, rather than outward, to the human community. So, married persons, as well as unmarried, must remain chaste according to their state in life.
For the Sacrament of Matrimony to be valid, there must be four conditions met. The couple must enter upon the union freely, totally, faithfully, and fruitfully. It must be free in that neither spouse is under coercion by the other or by a third party to marry. No shotgun weddings are valid. Besides giving their free consent to each other, they must be free to marry in that they must not have any “impediments” to marriage, such as being married. Their union must be total in that they intend to remain with each other until death and must give themselves totally to the other. Their life takes on a new meaning, in the sense that, after themselves, they are responsible for their spouse’s salvation. It must be faithful, not only in that the couple intends to marry for life, but that they are married by a deacon or priest, in the presence of at least two witnesses. It must be fruitful in that they intend to have children, whether or not they will indeed be able to.
The matter of the sacrament is the couple, the form is their vows. In the Latin Rite, the couple is also the minster of the sacrament. In the Eastern Rites, the priest or deacon (who can validly celebrate a marriage) are the ministers of the sacrament. This difference results from different accentuations in the sacrament, but not a fundamentally different conception of the sacrament.
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Divorce
The Catholic Church does not recognize divorce. Regarding marriage, Christ said: “So they are no longer two but one flesh. What therefore God has joined together, let not man put asunder” (Mt 19:6). The Church does not allow divorce under any circumstances because marriage is an indissoluble bond (until death). No spouses who enter upon a true marital union may ever retract on their vows.
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Annulments
In certain cases, a husband or wife seeking to separate from the other may receive an annulment. An annulment, again contrary to popular belief, is not a bill of divorce nor does it imply in any way the dissolution of the indissoluble union of marriage. Rather, it is an acknowledgement that the “marriage” which the couple in question entered upon previously was not a real marriage at all, and that therefore the supposed husband and wife were never married in the first place. Even if the couple went to the altar, if they lacked even one of the four necessary conditions (free, total, faithful, fruitful) at the time when they made their vows, their marriage never took place. There are Church tribunals that determine such cases.
However, if the couple had the proper intentions at the time of their wedding, their marriage did indeed take place and therefore is indissoluble. They cannot receive an annulment.
What about when one spouse is abusive: verbally, physically, sexually, etc., either to the spouse or to children. In such unfortunate circumstances, the children are always the most important. If one spouse is abusive to the children, the other spouse should seek to remove them from the situation immediately. A physical separation from the other spouse, perhaps even a permanent one, is not only recommended, but obligatory. However, this does not mean that the spouse can then marry someone else later, because they are still married to their spouse, no matter how abusive he or she has become. Even if that spouse “marries” someone else, the abused spouse cannot violate the marital covenant he or she entered into. Such situations are difficult and people going through them should be treated with especial compassion and assistance if necessary. However, their suffering does not make sin permissible.