Why is marriage precious?
Despite this, young people continue to wish to marry, and approximately fifty percent of them will do so successfully. Many of them cannot quite articulate what it is they intuit about the nobility of marriage, but they seem to know that if marriage was something less than themselves, like a revocable and private contract, there would be nothing to aspire to; for one does not aspire to what is lower, but only towards what is higher and loftier.
Indeed, young people want to aspire to what is truly larger than themselves, and marriage in the true sense of the word is larger than the self. What follows is an attempt to articulate some of the more essential points regarding the nature and dignity of the most fundamental and primary of institutions.
Unity is necessary
Unity and indissolubility are essential properties of marriage; for there is no marriage without them, just as there is no square without four equal sides and four right angles. A permanent union is precisely what a couple intend when they marry. If they do not, they might intend something, but they do not intend to marry.
In fact, indissolubility is nothing other than the good of marriage itself. Two people who intend to marry intend to give themselves to one another not partially, but entirely. And a total self-giving will necessarily include the giving of one's body, since the human person is a unity of spirit and matter. That is why marriage is a joining of two into a one-flesh union.
All love is a giving of oneself to some degree or another, but conjugal love is unique in that it is a love that is necessarily exclusive. If I give myself entirely to a person, there is nothing left over and at my disposal to give to someone else. Should there be, then I have not given myself entirely, but partially.
But giving oneself to another requires that the other is able to receive that self-giving. A person can only do so if he or she has an understanding of what is being given and what is demanded as a response. It follows that a certain level of intellectual maturity is required in order for a marriage to occur. It is necessary as well that a person actually be able to give himself or herself in return, and so a certain level of moral maturity is also required in order for marriage to be at all possible. If a person is unable to love in the highest sense of the word--willing that good befall another for the other's sake--that is, if a person is not able to love another on the level of the will, but only on an emotional level , then it is simply not possible for such a one to give himself or herself In marriage.
The mutual giving and receiving that is marriage also requires a free consent--for love is not love unless it is freely given. But this free consent is compromised in the case of fraud, when one of the partners withholds information about himself that had she known, she would not have consented to marriage (or vice versa), such as his true character, a criminal record, or a previous marriage, etc.
The marriage act
If both are willing to give themselves bodily to one another but are unable to actually receive bodily what they pledge to give, strictly speaking they are unable to marry. For example, a man and woman receive one another bodily through the act of sexual intercourse, which is why sexual union is called the marriage act. If for some reason they are unable to perform the marriage act, they are unable to consummate their marriage. That is why impotency and frigidity are impediments to marriage.
Both must also intend a permanent union, not a temporary one or one that leaves an opening for divorce. The reason is that when she gives her bodily self entirely to him and he gives his bodily self to her, she now has exclusive rights over his body, and he has exclusive rights over hers --if not, then no total self-giving has taken place. This self-giving is until death because it is only by his dying that she no longer has possession of his body, and vice versa. That is why vows that conclude "for as long as we both shall love," are not marriage vows at all.
A genuine and valid marriage also includes the intention to beget children. If she truly gave herself to him, and he gave his body to her without any reservations on the part of either one of them, that very intention includes an openness to children, because a child is the result of the physical union of both of them. Their mutual self-giving and one-flesh union continues on the bio-molecular level as sperm and oocyte join and become something else entirely, namely a child. To deliberately intend that this not occur is to intend not to be one body. Hence, it is to intend not to marry. 
Now a couple can discover that they are infertile yet still intend to become reproductively one organism (one body). Thus, infertility (the inability to have children) does not render a marriage invalid. Rather it is the intention not to have children that renders a marriage invalid, because that amounts to an intention not to become reproductively one organism (one body).
And so what is established when this mutual and total self-giving takes place? A unique, exclusive and permanent relationship, an indissoluble one-flesh union that has reference to children.
Marriage is irrevocable
Why is indissolubility the good of marriage itself? If both husband and wife consent to dissolving it, can they not do so?
If the marriage is a genuinely valid one--which is very often not the case, the answer is no. The reason is that what they have established is not sustained or perpetuated by their will, only initiated. It is something objective that exists independently of their will. Just as we cannot by an act of the will undo the fact that we are parents, so too is it impossible by an act of the will to undo the fact that we are spouses. Through the act of marital consent, a man and a woman give to one another a new and irrevocable identity. He becomes this woman's husband and she becomes this man's wife, and together they become spouses.
But why is it irrevocable? The reason is that if I can revoke what I give, then I have not given it entirely; what I gave was to some degree always in my possession. If I give you a stick and continue to hang on to it, I have not given all of it to you. But marriage is a total self-giving, which implies that he has given himself irrevocably to her, and she to him.  Allow me to attempt to explain this more fully.
What both of them consent to is the establishment of a union that exists until death separates them, not before. This giving is not like giving someone a house, for example, to be had until that person dies. In the latter case, the one who receives the gift could conceivably return it. But the only way to return a gift like a house that was gratuitously given is to "give it back." If I gave it to you and later on ask for it back, what I am asking is that you give me something, namely a gift, the same one that I previously gave you. Even if it is completely and irrevocably yours, the only way you can return it is by giving it to me as a gift.
But this does not work for marriage. The reason is that divorce is not a gift. It is not a positive self-giving, like the giving of a house that once belonged to another. It is a negative, a negation, not a positive.
What he has given in marriage is his very self until death, and she as well. It is precisely a permanent identity that both of them willed into existence for one another. That is what conjugal love is. But if she could give back what she received, she did not receive an irrevocable self-giving irrevocably, and vice versa, and one cannot give oneself irrevocably unless the giving is received irrevocably. By receiving his irrevocable self-giving "revocably," she simply does not allow him to give himself irrevocably, which means she does not receive what he offers her.
If she did not say "yes" to his total self-giving--and her "yes" requires nothing less than a total "yes;" or if he did not say "yes" to her total self-giving, which also requires nothing less than a total and irrevocable "yes," then they are not married. If they did receive one another irrevocably, they are married, and only death can sever the bond that they mutually and freely established. That is the nature of this particular kind of love, and that is why it is so noble and so momentous. Unlike a friendship, it establishes a permanent and irrevocable identity. If it did not, marriage would simply be one friendship alongside others. But it is indissolubility that makes the vocation of marriage so demanding and so lofty, and to succeed in marriage is a sign of heroic virtue. It is an achievement of the highest kind of human love.
THE SOCIAL NATURE OF MARRIAGE
An institution, not just a friendship
The marital consent establishes an organization or foundation, one that has an essential reference to the begetting and rearing of offspring. Marriage is thus an institution, not merely a friendship. It is not a private affair between two people. For society itself originates in marriage. Every one of us was introduced into the larger society through the more primary society of the family.
The family is thus prior to the civil community as a whole. That is why the state has no dominion over marriage. Marriage, rather, has a kind of dominion over the state. Indeed, the state has the right and duty to make laws that regulate and protect marriage because marriage is essentially a public affair, not a private one.
As was said, marriage is an institution, and what happens on the level of marriage and the family affects the civil community as a whole; for society suffers to the degree that marriages suffer, and it prospers to the degree that marriages are flourishing. But for society to protect and regulate marriage is for marriage and family to protect and regulate itself through the instrumentality of the state.
Family comes before the state
In this sense, parental rights are more original than the rights of the state with respect to marriage. Those who hold public office are at the service of the common good, and the family is the most fundamental condition that enables the members of the civil community as a whole to flourish. The duties of the state with respect to marriage are dictated by the rights and duties of spouses with respect to their marriage and family, not vice versa, unly totalitarianism has had and will continue to have problems with this idea.
Couples that marry and generate offspring and who love their children, rearing them to become good citizens, do an incalculable service to, the civil community as a whole. In fact, children incur a debt to their parents that they cannot fully remit. There is no human work more honourable and more important than that of being a good spouse and parent. But like anything noble and heroic, the work is hard. A successful marriage is an achievement of love, and love is difficult.
Sacrifice is not easy
It is difficult because love is essentially sacrificial, and human beings tend not to like making sacrifices. Husband and wife, both carriers of the wounds of Original Sin, will have to adjust to one another, get used to one another, and learn to live with one another. Each will have the difficult task of learning to relinquish his or her will often. Concupiscence--the inclination to seek the self first--is the biggest obstacle that threatens the success of every marriage.
But all marriages are tested, and every couple is destined to fall out of that initial but illusory and deceiving Eros that too many of us confuse with genuine conjugal love. The tests inevitably come in the form of desert periods that only a pure act of the will has the power to bring them through. The emotional intensity of Eros simply does not have the capacity to endure the heat of such trials, and many people simply do not have the willpower required to endure it. Their relationships will usually collapse here. But with each successful passage, a love emerges that is stronger, more refined, and richer than the love supported and penetrated by the glaze and sweetness of emotion that brought them to marriage in the first place.
Modern society abandons families
The sad fact about the post-modern era is that married couples cannot expect a great deal of help culturally and legally in remaining faithful to the covenant they so generously established. Essentially they have been left to themselves, to do as they wish or as one of them might wish, whether that turns out to be fidelity to the very end, or an open relationship, or a complete unilateral trade-in after a few months or twenty-five years. The legal community is completely indifferent either way. But there are non-secular supports that will go a long way in helping married couples achieve the noble end they have established for themselves. Baptized couples who have a valid marriage will be given the graces enabling them to be faithful spouses and loving parents.
But couples have to co-operate with those graces. A person who is willing to maintain a healthy mistrust of his own way of seeing things and who declares war on his own concupiscence is a person who is already more likely to succeed than not. A commitment to growing in humility and a regular prayer life and frequent reception of the sacraments--especially Confession--will only increase the chances of success. And in light of the fact that the divorce rate for couples practicing Natural Family Planning is less than 4%, the resolution not to contracept will in all likelihood render the chances of an irredeemable crash very slim. Couples that make it will have the further honour of helping to restore marriage on the political level, which can only help reverse the decline that has contributed to the incalculable suffering of innumerable innocent children.
(1.) There are two kinds of love within the human person. Firstly, love is a basic emotion of the concupiscible appetite, which is a sensitive appetite that man has in common with non-rational animals. This kind of love is ultimately self-love, which is loving something for what it does for me. The highest and specifically human kind of love is on the level of the will, which is not an emotion of the sensitive appetite, but the rational appetite. The will is able to move in a direction contrary to the movement of the passions. The highest kind of love is benevolence, or willing the good of another for the other's own sake, and not for the sake of what he or she does for me.
(2.) This of course does not mean that he may do anything he wants with her body. For he may not do whatever he wants with his own body, but is always and everywhere subject to the demands of natural and divine law. What it means is that she has given herself to him. Fie is bound to love her as he loves himself.
(3.) That is why contracepted intercourse cannot consummate a marriage, for contraception is an anti-procreative act, unlike sexual union during a non-fertile phase of a cycle, which is at best non-procreative and consistent with an openness to new life. The act of intercourse need not result in a conception in order to consummate a marriage, but it does need to be open to new life, and not intentionally closed to it.
(4.) "... we love one another truly and absolutely only when we love forever ..." (Angelus, 10 July 1994; L'Osservatore Romano English edition, 13 July 1994, p. 1). Also, "Love seeks to be definitive, it cannot be an arrangement 'until further notice.'" (Catechism of the Catholic Church, n. 1646).