Why does the Catholic Church have such a narrow definition of marriage?
The Church’s definition of marriage was revealed by God; so, it is perfect and cannot be changed to suit the passions of man.
The Church guards marriage, or holy matrimony very diligently because believes it to be a sacred thing: a divinely-ordained union between a man and a woman. Scripture reveals the dual nature of marriage: its unitive nature (i.e., the union of the spouses) and its procreative nature (i.e., openness to offspring). For example, in Genesis we see that God made man male and female; and that He called these two complementary sexes into union with one another in the great command to reproduce. “So God created man in his own image, in the image of God he created him; male and female he created them. And God blessed them, and God said to them, ‘Be fruitful and multiply’” (Genesis 1:27-28). “‘This at last is bone of my bones and flesh of my flesh,’” exclaims Adam at the first sight of Eve. “Therefore,” Scripture goes on to say, “a man leaves his father and his mother and cleaves to his wife, and they become one flesh” (Genesis 2:23-24).
Because God intended marriage to be a symbol of the covenant between Him and His people, a monogamous, indissoluble union is the ideal. Jesus restored marriage to this ideal during His ministry. When the Pharisees inquired as to whether or not divorce was permissible under any conditions, the Savior replied: “Have you not read that he who made them from the beginning made them male and female, and said, ‘For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh’? So they are no longer two but one flesh. What therefore God has joined together, let no man put asunder” (see Matthew 19:4-6 and Genesis 1:27; 2:24).
To this the Pharisees responded, “Why then did Moses command one to give a certificate of divorce, and to put her away?” The Lord answered: “For your hardness of heart Moses allowed you to divorce your wives, but from the beginning it was not so. And I say to you: whoever divorces his wife, except for unchastity, and marries another, commits adultery; and he who marries a divorced woman, commits adultery” (Matthew 19:7-9; emphasis added).
The “divorce” of which the Lord spoke should not to be confused with modern society’s notion of divorce. Jesus was referring to a legal separation without the freedom to remarry—the separation of the spouses, but not the dissolution of the marriage. Some, moreover, have argued that in making an exception for occasions of “unchastity” Jesus is permitting divorce. The original Hebrew word here, though, is pornea, which is probably more accurately translated as “fornication,” implying a sin that took place prior to the marriage, thus rendering the marriage null and void. The Lord, then, is not permitting the break up of a valid marriage, but is recognizing that a union may be rendered invalid by a defect that was brought into it from the start. So, this would agree more with the concept of annulments, than with divorce.
In the same passage, moreover, Jesus expressly forbid remarriage, saying, “He who marries a divorced woman commits adultery” (Matthew 19:9; cf. 5:32). He said also, “What therefore God has joined together, let no man put asunder;” and, regarding divorce, “from the beginning it was not so” (19:6, 8). In the Gospel of Mark, Jesus said, “Whoever divorces his wife and marries another, commits adultery with her; and if she divorces her husband and marries another, she commits adultery” (10:11-12; see also Luke 16:18).
Likewise, in his First Letter to the Corinthians (7:10 -11), Saint Paul writes, “To the married I give the charge, not I but the Lord, that the wife should not separate from her husband (but if she does, let her remain single or else be reconciled with her husband)—and that the husband should not divorce his wife.” According to Paul, in the same letter to the Corinthians, the marital bond can only be broken by death (7:39).
The Church has always seen in marriage a deep symbolism and extraordinary virtue.
Jesus compared Heaven to a “wedding banquet” (Matthew 22:2 and 25:10), and his first public miracle–of turning water into wine–was performed at a wedding feast (see John 2:1).
The earliest Christian historical writings beyond Scripture likewise defend the sanctity and indissolubility of marriage. For example, Saint Ignatius of Antioch, writing in about A.D. 107, said, “It is proper for men and women who wish to marry to be united with the consent of the bishop, so that their marriage will be acceptable to the Lord, and not entered upon for the sake of lust. Let all things be done for the honor of God” (Letter to Polycarp 5:2).
In about the year 150, Saint Justin the Martyr commenting on Matthew 19:9, wrote, “According to our Teacher, just as they are sinners who contract a second marriage, even though it be in accord with human law, so also are they sinners who look with lustful desire at a woman” (First Apology 15). At about the same time, Athenagoras of Athens wrote, “We hold that a man should either remain as he is born or else marry only once. For a second marriage is a veiled adultery” (A Plea for the Christians 33). “How shall we suffice,” wrote Tertullian at the beginning of the third century, “for the telling of that happiness of that marriage which the Church arranges, which the sacrifice (i.e., the Eucharist) strengthens, on which the blessing sets a seal, which the angels proclaim, and which has the Father’s approval?” (To My Wife 2:8:6). At the same time, Saint Clement of Alexandria, citing Christ’s teaching in Matthew 5:32, defined adultery as entering into a second marriage while the former spouse is still living (Stromateis 2:23:145:3)