Cardinal Donald Wuerl is archbishop of Washington.

This is a significant moment in our public conversation on marriage. By ruling a key part of the Defense of Marriage Act unconstitutional and choosing not to rule on the question of same-sex marriage in California, the Supreme Court essentially declared that the federal government may not set parameters for the definition of marriage but, instead, must leave that power to the states.

This means that the important debate about the meaning of marriage is destined to continue. Some have framed this debate in terms of “equality.” That rings with a certain American appeal. Everyone wants to be treated equally, with the love and respect due all people. But focusing on “marriage equality” gets the question wrong. Equality requires treating like cases alike. We need to determine whether we have “like cases” at all. If we want to address the principle of equality correctly, we need to get to the truth of marriage first.

Arguing that the law, for equality’s sake, should recognize two men or two women as “married” presumes that these pairs are the same as one man and one woman and that marriage is simply a committed relationship of any adults. All of this raises the question: What is the nature of marriage?

Marriage is the word used in many translations across human history to signify the permanent, faithful and fruitful union of one man and one woman. It is the only institution that brings a man and a woman together in a partnership for life directed toward their mutual support and the generation and education of children. This is a human community that predates government. Its meaning is something to be recognized and protected, not reconstructed. Its simplicity is compelling. Its significance, both personal and public, is immeasurable. What promise between two people holds the same weight and consequence as that of a man and a woman who give themselves to each other for life with a view toward creating new life so that humanity might continue?

Marriage goes to the nature of the human person. Even if individual men and women are unable to have children for some reason, still it is the nature of man and woman to complement each other in such a way that is fruitful and capable of children. Two persons of the same sex, on the other hand, can never have children by the very nature of such a union.

No matter what a court, legislator, president or voter may claim to the contrary, the essence of marriage cannot be redefined. Its meaning is intrinsic, grounded in human nature and discoverable by human reason with or without the aid of faith.

A culture based on the truth of marriage affirms that men and women are equally important, that they have equal dignity but are not the same. The recognition of the difference between a man and a woman is neither discrimination nor bigotry. It is a statement of reality, of fact.

What the court has determined demonstrates the limits of civil legislation. We all recognize that the word “marriage” is being used in many different ways. All that civil government can do is address the legal consequences of any specific union it has chosen to call marriage. While there are many other words to describe other human unions, “marriage,” in its intrinsic meaning and basic integrity, will continue to be understood by most people as the coming together of a man and woman committed to live together with the possibility to generate and raise children.

Far from settling the debate over the meaning of marriage, the Supreme Court decisions have simply reminded all of us that there is a great difference between what a law can decree and what God has created.

Read more from PostOpinions:

Cardinal Donald Wuerl: Protecting our Catholic conscience in the public square

Charles Krauthammer: Nationalized gay marriage is now inevitable

The Post’s View: A triumph for same-sex equality

Ruth Marcus: Why I hope Scalia is right on same-sex marriage

E.J. Dionne: The Supreme Court uses judicial activism for conservative ends

‘Smart’ or ‘outrageous’? Gay rights advocates and critics respond to Court rulings