Mary and I are extremely close in the ways that count, even though we don’t talk every day or consider ourselves “best friends.” We both have busy lives, jobs, pets, and travel schedules; and we have many differences too. Twenty years ago these differences divided us; now they no longer do. And yet the differences themselves persist.

Mary is athletic; I’m not. She’s much more libertarian, though socially liberal; I’m more conservative. She has the cool modern furniture; my house is nearly a century old and my decorating style is traditional. But these differences don’t matter much to anyone, including us.

Yet there is one that does. It is my deep conviction that the complementarity of gender—man and woman—and the possibility of new life that may result from their union aren’t accidental but essential to the institution of marriage. Until about fifteen years ago, most people, gay and straight alike, would probably have agreed with me. Today I’m well aware that many no longer do, including my sister.

I don’t come to my understanding of marriage because, as some will undoubtedly assume, because I am a “bigot,” or have animus toward gays and lesbians. I have been reflecting on the issue in a philosophical and historical way for more than a decade now. I know the Supreme Court case law regarding gay and lesbian rights and gay marriage backwards and forwards. I take the arguments for gay marriage very seriously.

And I don’t hold my position in a defensive or angry way either. I’m well aware that the Court is likely to rule in favor of a national right to gay marriage in June of this year. I know I won’t convince many people—or anyone—who isn’t already inclined to agree with me. Yet I can’t abandon my view, nor can the silent millions of people who agree with me. It is a deep and considered conviction about the nature of reality, analogous to the deep conviction that many other people now hold about “marriage equality” as a fundamental moral truth.

So what does this mean for my relationship with Mary? Should she hate me for what I think? Should I in turn hate her because she is gay? Nothing could be further from our minds.

Because here’s the crux of the matter: I love my sister not for (or against) her sexuality, but for her total personality, which includes humor, intelligence, beauty, kindness, and generosity. In a word, I love her character.

Mary and I live in a pluralist age when people of goodwill often hold radically different views. This calls, I think, for tolerance of the old-fashioned kind, not persecution of those who differ. It calls for patience and perhaps even persuasion, But the persuasion I have in mind is a humble kind of dialogue that approaches others with dignity and entertains the possibility that they, not I, have a greater purchase on the truth. Often, neither side can be persuaded, and so the differences persist. If this is the case, then tolerance calls for civility despite differences. At root, I believe it calls for love.