 In contrast to the ancients, whose philosophical discussion of sex and sexual love was not confined to marriage, Christian philosophers introduced a new focus on marriage as the sole permissible context for sex, marking a shift from viewing marriage as primarily a political and economic unit. St. Augustine (354–430), following St. Paul, condemns sex outside marriage and lust within it. “[A]bstinence from all sexual union is better even than marital intercourse performed for the sake of procreating,” and the unmarried state is best of all (The Excellence of Marriage, ca. 401, §6, 13/15). But marriage is justified by its goods: “children, fidelity [between spouses], and sacrament.” Although procreation is the purpose of marriage, marriage does not morally rehabilitate lust. Instead, the reason for the individual marital sexual act determines its permissibility. Sex for the sake of procreation is not sinful, and sex within marriage solely to satisfy lust is a pardonable (venial) sin. As marital sex is preferable to “fornication” (extra-marital sex), spouses owe the “marriage debt” (sex) to protect against temptation, thereby sustaining mutual fidelity (Marriage and Desire, Book I, ca. 418–19, §7, 8, 17/19, 14/16).