The Parson's Tale, perhaps the most didactic part of the Canterbury Tales, provides helpful insight into the medieval world's definition and understanding of lechery. According to the Christian doctrine of the period, the concept of lechery was broad and sobering:

Now let us speak of that stinking sin of Lechery which is called adultery of married folk, which is to say, if one of them be married, or both.. And God not only forbade adultery in deed, but he also commanded that thou shalt not covet thy neighbor's wife. "In this behest," says Saint Augustine, "is forbidden all lecherous desires." See what Saint Matthew says in his gospel: "Whosover shall look on a woman to lust after her, hath already committed adultery with her in his heart." (Parson's Tale , Lines 842-64)

The quotation from the gospel of Matthew is most provocative. Christ asserts that lustful desire, independent of actual copulation, is adulterous.