II. The Definition of Sin

From The Catechism of the Catholic Church

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