Sin is present in human history; any attempt to ignore it or to give this dark reality other names would be futile. To try to understand what sin is, one must first recognize the profound relation of man to God, for only in this relationship is the evil of sin unmasked in its true identity as humanity’s rejection of God and opposition to him, even as it continues to weigh heavy on human life and history.
Only the light of divine Revelation clarifies the reality of sin and particularly of the sin committed at mankind’s origins. Without the knowledge Revelation gives of God we cannot recognize sin clearly and are tempted to explain it as merely a developmental flaw, a psychological weakness, a mistake, or the necessary consequence of an inadequate social structure, etc. Only in the knowledge of God’s plan for man can we grasp that sin is an abuse of the freedom that God gives to created persons so that they are capable of loving him and loving one another. With the progress of Revelation, the reality of sin is also illuminated. Although to some extent the People of God in the Old Testament had tried to understand the pathos of the human condition in the light of the history of the fall narrated in Genesis, they could not grasp this story’s ultimate meaning, which is revealed only in the light of the death and Resurrection of Jesus Christ. We must know Christ as the source of grace in order to know Adam as the source of sin. the Spirit-Paraclete, sent by the risen Christ, came to “convict the world concerning sin”, by revealing him who is its Redeemer.
The doctrine of original sin is, so to speak, the “reverse side” of the Good News that Jesus is the Saviour of all men, that all need salvation and that salvation is offered to all through Christ. the Church, which has the mind of Christ, knows very well that we cannot tamper with the revelation of original sin without undermining the mystery of Christ. The account of the fall in Genesis 3 uses figurative language, but affirms a primeval event, a deed that took place at the beginning of the history of man. Revelation gives us the certainty of faith that the whole of human history is marked by the original fault freely committed by our first parents.
From the Catechism of the Catholic Church 386-390