When St. Paul wanted to explain the relationship between Christ and his Church, he used the image of the bridegroom and the bride, because he knew that this image would resonate through all ages and in all cultures. As Christians we believe that marriage is a natural institution, which has existed from the beginning and was always part of God's plan for mankind -- "therefore a man shall leave his father and mother and cleave to his wife and they shall become one flesh and what God has joined together let no man put asunder."

Marriage didn't just happen. It was created by God for the good of man and to be an image of God's love for his people. Marriage is a covenant relationship, a sign of the bond between Israel and God, between Christ and the Church. In marriage, husband and wife become one flesh in the act of marital union. Through that act they are able to conceive children -- the fruit of their love. In the child, the two become one flesh in the joining of their DNA to form a new person. Jesus tells us that God meant marriage to be permanent. We know from Scripture that he meant it to be faithful. However, even without the witness of scripture, all peoples in all cultures have recognized the importance of marriage, parenthood, and faithfulness, at least until now.

While it is understandable that same-sex couples would envy those who are married, their demand that their relationships be recognized as marriages is not a plea to enter a structure from which they have been barred, but a demand that the structure be demolished.

Marriage is not a right, it is a reality. To call something that is not a marriage and cannot be a marriage a marriage is to lie. Two people of the same sex cannot consummate their love in the one act that makes a marriage and is open to the conception of a child that is the biological child of both.

For those who don't understand how different a same-sex relationship is from the marital union of husband and wife, I could recommend "Beyond Monogamy" a study done by gay men about long-term male same-sex relationships. The study demonstrates what has been long known, namely that same-sex male relationships are rarely faithful and regularly find ways to incorporate outside liaisons. I warn anyone who doesn't take my word for this and decides to look up the study on the Internet, the contents are unpleasantly shocking. Numerous gay male writers have suggested that the kind of infidelity common among them would improve marriage between a man and a woman. Other gay advocates openly call for the destruction of all "heterosexist" institutions.

If you want to understand why same-sex couples should not be encouraged to acquire children, read the new study "My Daddy's Name Is Donor." The study compares children born through artificial insemination donor to married couples, single mothers, and same-sex couples, with children adopted immediately after birth, and those born to married couples. It found that those conceived by artificial insemination donor were worse off over time. Separation of a child from one or both of his biological parents is always perceived by the child as a loss. A family headed by a same-sex couple by definition lacks either a father or a mother. Thus a child in these families has been twice harmed, first losing a biological parent and second being deprived of a father or a mother. Unfortunately, the negative effects of the baby boom among same-sex couples will not be fully known for a generation and then it will be too late.

The demand for the redefinition of marriage flows from the latest heresy, namely that sex difference doesn't matter, and society should make no distinctions between men and women. This goes against common sense and everything that science has learned about the human person. In defending marriage as the union between one man and one woman we are defending the very nature of marriage, the good of children, and the truth about the differences between the sexes.

Why have so many people fallen for the claim that sex difference is irrelevant and changing the definition of marriage is no big deal? Probably because many people feel sorry for persons with same-sex attraction. They wrongly believe that persons with same-sex attraction were born that way and can't change, even though there is substantial evidence that neither is true. If same-sex attraction were genetic, then one would expect that identical twins would virtually always have the same pattern of sexual attraction, but study after study have shown this is not the case. There is substantial evidence that same-sex attraction begins with a failure to have key developmental needs -- attachment, separation, and identification -- met in the first years of life. This may be complicated by a history of abuse or sexual exploitation. Change, while extremely difficult, is possible. With God's grace it is possible to live celibately.

The Church has made it clear that same-sex intimacy is always contrary to God's plan. No matter what the state says this isn't going to change. No matter what judges, say marriage will always be the union of one man and one woman.

Dale O'Leary is an internationally recognized lecturer and author of "The Gender Agenda: Redefining Equality."