The consequences of Adam’s sin for humanity
402 All men are implicated in Adam’s sin, as St. Paul affirms: “By one man’s disobedience many (that is, all men) were made sinners”: "sin came into the world through one man and death through sin, and so death spread to all men because all men sinned."289 The Apostle contrasts the universality of sin and death with the universality of salvation in Christ. "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."290
403 Following St. Paul, the Church has always taught that the overwhelming misery which oppresses men and their inclination towards evil and death cannot be understood apart from their connection with Adam’s sin and the fact that he has transmitted to us a sin with which we are all born afflicted, a sin which is the “death of the soul”.291 Because of this certainty of faith, the Church baptizes for the remission of sins even tiny infants who have not committed personal sin.292
404 How did the sin of Adam become the sin of all his descendants? The whole human race is in Adam “as one body of one man”.293 By this “unity of the human race” all men are implicated in Adam’s sin, as all are implicated in Christ’s justice. Still, the transmission of original sin is a mystery that we cannot fully understand. But we do know by Revelation that Adam had received original holiness and justice not for himself alone, but for all human nature. By yielding to the tempter, Adam and Eve committed a personal sin, but this sin affected the human nature that they would then transmit in a fallen state.294 It is a sin which will be transmitted by propagation to all mankind, that is, by the transmission of a human nature deprived of original holiness and justice. And that is why original sin is called “sin” only in an analogical sense: it is a sin “contracted” and not “committed” - a state and not an act.
405 Although it is proper to each individual,295 original sin does not have the character of a personal fault in any of Adam’s descendants. It is a deprivation of original holiness and justice, but human nature has not been totally corrupted: it is wounded in the natural powers proper to it, subject to ignorance, suffering and the dominion of death, and inclined to sin - an inclination to evil that is called concupiscence". Baptism, by imparting the life of Christ’s grace, erases original sin and turns a man back towards God, but the consequences for nature, weakened and inclined to evil, persist in man and summon him to spiritual battle.
406 The Church’s teaching on the transmission of original sin was articulated more precisely in the fifth century, especially under the impulse of St. Augustine’s reflections against Pelagianism, and in the sixteenth century, in opposition to the Protestant Reformation. Pelagius held that man could, by the natural power of free will and without the necessary help of God’s grace, lead a morally good life; he thus reduced the influence of Adam’s fault to bad example. The first Protestant reformers, on the contrary, taught that original sin has radically perverted man and destroyed his freedom; they identified the sin inherited by each man with the tendency to evil (concupiscentia), which would be insurmountable. The Church pronounced on the meaning of the data of Revelation on original sin especially at the second Council of Orange (529)296 and at the Council of Trent (1546).297
A hard battle. . .
407 The doctrine of original sin, closely connected with that of redemption by Christ, provides lucid discernment of man’s situation and activity in the world. By our first parents’ sin, the devil has acquired a certain domination over man, even though man remains free. Original sin entails “captivity under the power of him who thenceforth had the power of death, that is, the devil”.298 Ignorance of the fact that man has a wounded nature inclined to evil gives rise to serious errors in the areas of education, politics, social action299 and morals.
408 The consequences of original sin and of all men’s personal sins put the world as a whole in the sinful condition aptly described in St. John’s expression, “the sin of the world”.300 This expression can also refer to the negative influence exerted on people by communal situations and social structures that are the fruit of men’s sins.301
409 This dramatic situation of "the whole world [which] is in the power of the evil one"302 makes man’s life a battle:
The whole of man’s history has been the story of dour combat with the powers of evil, stretching, so our Lord tells us, from the very dawn of history until the last day. Finding himself in the midst of the battlefield man has to struggle to do what is right, and it is at great cost to himself, and aided by God’s grace, that he succeeds in achieving his own inner integrity.303
IV. “YOU DID NOT ABANDON HIM TO THE POWER OF DEATH”
410 After his fall, man was not abandoned by God. On the contrary, God calls him and in a mysterious way heralds the coming victory over evil and his restoration from his fall.304 This passage in Genesis is called the Protoevangelium (“first gospel”): the first announcement of the Messiah and Redeemer, of a battle between the serpent and the Woman, and of the final victory of a descendant of hers.
411 The Christian tradition sees in this passage an announcement of the “New Adam” who, because he “became obedient unto death, even death on a cross”, makes amends superabundantly for the disobedience, of Adam.305 Furthermore many Fathers and Doctors of the Church have seen the woman announced in the Protoevangelium as Mary, the mother of Christ, the “new Eve”. Mary benefited first of all and uniquely from Christ’s victory over sin: she was preserved from all stain of original sin and by a special grace of God committed no sin of any kind during her whole earthly life.306
412 But why did God not prevent the first man from sinning? St. Leo the Great responds, "Christ’s inexpressible grace gave us blessings better than those the demon’s envy had taken away."307 And St. Thomas Aquinas wrote, "There is nothing to prevent human nature’s being raised up to something greater, even after sin; God permits evil in order to draw forth some greater good. Thus St. Paul says, ‘Where sin increased, grace abounded all the more’; and the Exsultet sings, ‘O happy fault,. . . which gained for us so great a Redeemer!’"308
vatican.va/archive/ccc_css/archive/catechism/p1s2c1p7.htm#399