Catechism of the Catholic Church
1849 Sin is an offense against reason, truth, and right conscience; it is failure in genuine love for God and neighbor caused by a perverse attachment to certain goods. It wounds the nature of man and injures human solidarity. It has been defined as "an utterance, a deed, or a desire contrary to the eternal law." 121
1850 Sin is an offense against God: "Against you, you alone, have I sinned, and done that which is evil in your sight." 122 Sin sets itself against God's love for us and turns our hearts away from it. Like the first sin, it is disobedience, a revolt against God through the will to become "like gods," 123 knowing and determining good and evil. Sin is thus "love of oneself even to contempt of God." 124 In this proud self- exaltation, sin is diametrically opposed to the obedience of Jesus, which achieves our salvation. 125
1851 It is precisely in the Passion, when the mercy of Christ is about to vanquish it, that sin most clearly manifests its violence and its many forms: unbelief, murderous hatred, shunning and mockery by the leaders and the people, Pilate's cowardice and the cruelty of the soldiers, Judas' betrayal - so bitter to Jesus, Peter's denial and the disciples' flight. However, at the very hour of darkness, the hour of the prince of this world, 126 the sacrifice of Christ secretly becomes the source from which the forgiveness of our sins will pour forth inexhaustibly.
English Translation of the Cathechism of the Catholic Church for the United States of America © 1997, United States Catholic Conference, Inc.