Gilbert Keith Chesterton (1874-1936) was one of the most prolific writers of the twentieth century and was, like Lewis, a Christian. According to the American Chesterton Society, "He wrote a hundred books, contributions to 200 more, hundreds of poems, including the epic Ballad of the White Horse, five plays, five novels, and some two hundred short stories, including a popular series featuring the priest-detective, Father Brown. In spite of his literary accomplishments, he considered himself primarily a journalist. ... Chesterton was equally at ease with literary and social criticism, history, politics, economics, philosophy, and theology. His style is unmistakable, always marked by humility, consistency, paradox, wit, and wonder."
Lewis is referring to statements Chesterton made in "A Defence of Rash Vows," which appears in The Defendant: "The revolt against vows has been carried in our day even to the extent of a revolt against the typical vow of marriage. It is most amusing to listen to the opponents of marriage on this subject. They appear to imagine that the ideal of constancy was a yoke mysteriously imposed on mankind by the devil, instead of being, as it is, a yoke consistently imposed by all lovers on themselves. They have invented a phrase, a phrase that is a black and white contradiction in two words—'free-love'—as if a lover ever had been, or ever could be, free. It is the nature of love to bind itself, and the institution of marriage merely paid the average man the compliment of taking him at his word" (emphasis added).