By Anthony Esolen

"God is love," says Saint John, and "Our God is a consuming fire," says the author of Hebrews, for "it is a terrible thing to fall into the hands of the living God."

But we have fallen. We are sinners, slow of mind and hard of heart, nor do we rightly know what love is. We are apt to take it for our sentiments. If you think that hardness of heart is incompatible with sentimentality, consider that Jean-Jacques Rousseau, the sentimentalist author of Emile, on the education of children, abandoned the five illegitimate children of his own to an orphanage in Paris.

I've never met a person who couldn't justify the wrong he had done because of some kind of love. Stalin could say that he loved Russia, and that he burnt out his soul with that love. Other people could take him at his word. You might check out, for example, the fulsome tribute that the otherwise brilliant W. E. B. Du Bois wrote to commemorate the death of Stalin.

It makes that mass murderer out to be an alloy of iron commitment to justice, and warm feeling for downtrodden man who, Du Bois says, stands in solemn acclaim for this courteous leader, conciliatory whenever he could be, inflexible only when he must be. Stalin - loving and beloved.

Dante says, in Purgatory, that love - meaning desire - is the seedbed of all the good we do and all the evil. That's a corrective to what his predecessors in love poetry sometimes seemed to say, that erotic passion of the noble and courteous kind, whether within marriage or outside it, is its own justification. A desire may, considered abstractly, be good, but it may be evil in the form it takes when we act upon it.

Most of the great poetry of the Middle Ages and the Renaissance is devoted to just this problem of love. Shakespeare says, with only apparent contradiction, that "Love is not love / Which alters when it alteration finds." He does not say "It" is not love, but "love" is not love. That's no mere play on words. He is distinguishing between love and love, between something that we call love, and that we mostly feel as love and mistake for love, and what love really is.

People in the heat of lust talk much of love. But "such love is hate," says the poet Edmund Spenser, who was surely no prig. After he had written and published his first three books of The Faerie Queene, he says he got some sharp criticism from people who objected to his poetry of love, thinking that it might lead youth astray.

"Such ones ill judge of love, that cannot love," says he, "Nor in their frozen hearts feel kindly flame." The word "kindly" there means "natural," "according to kind," as God created us in the beginning, in our kinds, and commanded us to be fruitful and to multiply. It names the prime end for sexual desire.

John Milton, who took heat from both high church Anglican and low church Presbyterian, defended his decision to portray Adam and Eve in all the naked glory of their innocence and their passionate marital love:

Hail, wedded Love, mysterious law, true source Of human offspring, sole propriety In Paradise of all things common else! By thee adulterous lust was driven from men Among the bestial herds to range; by thee, Founded in reason, loyal, just, and pure, Relations dear, and all the charities Of father, son, and brother, first were known. Far be it that I should write thee sin or blame, Or think thee unbefitting holiest place, Perpetual fountain of domestic sweets, Whose bed is undefiled and chaste pronounced, Present, or past, as saints and patriarchs used.

In affirming that innocence would have made relations between Adam and Eve more delightful, not less, Milton is careful to show us the dampening and glooming effects of sin. For the first thing that Adam and Eve do after the fall is to make love, not in their sacred marital bower, but in the open air, and then they fall into a drunken kind of sleep, one that brings no rest.

That this seal of their sin was not an act of love, though they are married and though t...