@michael-kaw
http://www.vatican.va/archive/ccc_css/archive/catechism/p3s1c1a8.htm
II. THE DEFINITION OF SIN
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
1862 One commits venial sin when, in a less serious matter, he does not observe the standard prescribed by the moral law, or when he disobeys the moral law in a grave matter, but without full knowledge or without complete consent.
1863 Venial sin weakens charity; it manifests a disordered affection for created goods; it impedes the soul’s progress in the exercise of the virtues and the practice of the moral good; it merits temporal punishment. Deliberate and unrepented venial sin disposes us little by little to commit mortal sin. However venial sin does not break the covenant with God. With God’s grace it is humanly reparable. "Venial sin does not deprive the sinner of sanctifying grace, friendship with God, charity, and consequently eternal happiness."134
While he is in the flesh, man cannot help but have at least some light sins. But do not despise these sins which we call “light”: if you take them for light when you weigh them, tremble when you count them. A number of light objects makes a great mass; a number of drops fills a river; a number of grains makes a heap. What then is our hope? Above all, confession.135
IN BRIEF
1870 “God has consigned all men to disobedience, that he may have mercy upon all” (Rom 11:32).
1871 Sin is an utterance, a deed, or a desire contrary to the eternal law (St. Augustine, Faust 22
L 42, 418). It is an offense against God. It rises up against God in a disobedience contrary to the obedience of Christ.
1872 Sin is an act contrary to reason. It wounds man’s nature and injures human solidarity.
1873 The root of all sins lies in man’s heart. The kinds and the gravity of sins are determined principally by their objects.
1874 To choose deliberately - that is, both knowing it and willing it - something gravely contrary to the divine law and to the ultimate end of man is to commit a mortal sin. This destroys in us the charity without which eternal beatitude is impossible. Unrepented, it brings eternal death.
1875 Venial sin constitutes a moral disorder that is reparable by charity, which it allows to subsist in us.
1876 The repetition of sins - even venial ones - engenders vices, among which are the capital sins.
