Original Sin
From the Compendium Catechism:

72. What was the original condition of the human person according to the plan of God?

In creating man and woman God had given them a special participation in his own divine life in holiness and justice. In the plan of God they would not have had to suffer or die. Furthermore, a perfect harmony held sway within the human person, a harmony between creature and Creator, between man and woman, as well as between the first human couple and all of creation.

73. How should we understand the reality of sin?

Sin is present in human history. This reality of sin can be understood clearly only in the light of divine revelation and above all in the light of Christ the Savior of all. Where sin abounded, he made grace to abound all the more.

74. What was the fall of the angels?

This expression indicates that Satan and the other demons, about which Sacred Scripture and the Tradition of the Church speak, were angels, created good by God. They were, however, transformed into evil because with a free and irrevocable choice they rejected God and his Kingdom, thus giving rise to the existence of hell. They try to associate human beings with their revolt against God. However, God has wrought in Christ a sure victory over the Evil One.

75. What was the first human sin?

When tempted by the devil, the first man and woman allowed trust in their Creator to die in their hearts. In their disobedience they wished to become “like God” but without God and not in accordance with God (Genesis 3:5). Thus, Adam and Eve immediately lost for themselves and for all their descendants the original grace of holiness and justice.

76. What is original sin?

Original sin, in which all human beings are born, is the state of deprivation of original holiness and justice. It is a sin “contracted” by us not “committed”; it is a state of birth and not a personal act. Because of the original unity of all human beings, it is transmitted to the descendants of Adam “not by imitation, but by propagation”. This transmission remains a mystery which we cannot fully understand.

77. What other consequences derive from original sin?

In consequence of original sin human nature, without being totally corrupted, is wounded in its natural powers. It is subject to ignorance, to suffering, and to the dominion of death and is inclined toward sin. This inclination is called concupiscence.

78. After the first sin, what did God do?

After the first sin the world was inundated with sin but God did not abandon man to the power of death. Rather, he foretold in a mysterious way in the “Protoevangelium” (Genesis 3:15) that evil would be conquered and that man would be lifted up from his fall. This was the first proclamation of the Messiah and Redeemer. Therefore, the fall would be called in the future a “happy fault” because it “gained for us so great a Redeemer” (Liturgy of the Easter Vigil).