The ninth commandment requires that one overcome carnal concupiscence in thought and in desire. The struggle against such concupiscence entails purifying the heart and practicing the virtue of temperance.
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2514. St. John distinguishes three kinds of covetousness or concupiscence: lust of the flesh, lust of the eyes, and pride of life.300In the Catholic catechetical tradition, the ninth commandment forbids carnal concupiscence; the tenth forbids coveting another's goods.
2515. Etymologically, "concupiscence" can refer to any intense form of human desire. Christian theology has given it a particular meaning: the movement of the sensitive appetite contrary to the operation of the human reason. the apostle St. Paul identifies it with the rebellion of the "flesh" against the "spirit."301Concupiscence stems from the disobedience of the first sin. It unsettles man's moral faculties and, without being in itself an offense, inclines man to commit sins.302
2516. Because man is a composite being, spirit and body, there already exists a certain tension in him; a certain struggle of tendencies between "spirit" and "flesh" develops. But in fact this struggle belongs to the heritage of sin. It is a consequence of sin and at the same time a confirmation of it. It is part of the daily experience of the spiritual battle:
For the Apostle it is not a matter of despising and condemning the body which with the spiritual soul constitutes man's nature and personal subjectivity. Rather, he is concerned with the morally good or bad works, or better, the permanent dispositions - virtues and vices - which are the fruit of submission (in the first case) or of resistance (in the second case) to the saving action of the Holy Spirit. For this reason the Apostle writes: "If we live by the Spirit, let us also walk by the Spirit."303
2528. "Everyone who looks at a woman lustfully has already committed adultery with her in his heart" (Mt 5:28).
2529. The ninth commandment warns against lust or carnal concupiscence.
2530. The struggle against carnal lust involves purifying the heart and practicing temperance.