The clearest revelation on original sin is found in the Epistles of St. Paul, especially Romans 5:12-20. St. Paul writes:
Then as one man's trespass led to condemnation for all men, so one man's act of righteousness leads to acquittal and life for all men. For as by one man's disobedience many were made sinners, so by one man's obedience many will be made righteous. [Rom 5:18-19]
Adam's original disobedience made us all sinners, while Christ's obedience on the Cross saves us from our sins. St. Paul also writes:
Therefore as sin came into the world through one man and death through sin, and so death spread to all men because all men sinned. [Rom 5:12]
Adam's sin also brought death; however, death here should not be merely thought of in terms of bodily death as that which all animals experience but in a spiritual sense, as in the loss of eternal life (CCC 403). This passage also implies that even though Adam brought death into the world, we are also responsible since we all sinned. Elsewhere St. Paul writes:
For as by a man came death, by a man has come also the resurrection of the dead. For as in Adam all die, so also in Christ shall all be made alive. [1 Cor 15:21-22]
According to these passages, we inherited sin and death as a result of Adam's sin. This is why St. Paul reminds us that "we were by nature children of wrath." [Eph 2:3]
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Original Sin :: Catholic News Agency