The Ninth Commandment
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"You shall not covet your neighbor's wife" (Ex 20:17).
Three Types of Illicit Desires (2514)
Everyone who looks at a woman lustfully has already committed adultery with her in his heart" (Mt 5:28).
St. John lists three types of concupiscence, lust of the flesh, lust of the eyes, and the pride of life (Jn 2:16). In Catholic Tradition, the ninth commandment forbids lust (carnal concupiscence).
Defining "Concupiscence" (2515)
"Concupiscence" refers to any intense form of human desire. In Christian theology, concupiscence means a movement of the sensitive appetite which is against human reason. Paul calls it a rebellion of the flesh against the spirit. Concupiscence, which comes from original sin, unsettles man's moral powers and inclines him to sin (although not itself being a sin).
The Flesh Wars against the Spirit (2516)
Because man is a composite being (spirit and body) a certain tension exists. There is a struggle of tendencies between "spirit" and "flesh." This struggle comes from the consequences of sin.
St. Paul did not condemn the body. Rather he was concerned with the body's good works which come from submission to the Spirit or its bad works which come from resistance to the Spirit (Pope John Paul II).