I have been a Catholic for quite a while, and since going to college I have become a bit more interested than I was previously in ensuring that my faith is the correct one. The question of Original Sin came up pretty quickly in my examinations, and I found that I had no explanation for it. First of all, it is clear from Church doctrine that sin is Voluntary.
Original sin is voluntary in this or that man/woman born of Adam not by his own will but by the will of his first parent just as the action of one member of the body, of the hand for instance, is voluntary not by the will of that hand, but by the will of the soul, the first mover of the members. Accordingly, in explaining how original sin is transmitted to all the posterity of Adam and Eve and how all men are implicated in Adam’s sin, the CCC#404 says “The whole human race is in Adam as one body of one man.” And the footnote points us to the De Malo of St Thomas Aquinas. Here I will quote from St Thomas’ Summa Theologica which is the same explanation he gives in De Malo. It is a remarkable piece of teaching and insight:
In endeavoring to explain how the sin of our first parent could be transmitted by way of origin to his descendants, various writers have gone about it in various ways…
Therefore we must explain the matter otherwise by saying that all men born of Adam may be considered as one man, inasmuch as they have one common nature, which they receive from their first parents; even as in civil matters, all who are members of one community are reputed as one body, and the whole community as one man. Indeed Porphyry says (Praedic., De Specie) that “by sharing the same species, many men are one man.” Accordingly the multitude of men born of Adam, are as so many members of one body. Now the action of one member of the body, of the hand for instance, is voluntary not by the will of that hand, but by the will of the soul, the first mover of the members. Wherefore a murder which the hand commits would not be imputed as a sin to the hand, considered by itself as apart from the body, but is imputed to it as something belonging to man and moved by man’s first moving principle. In this way, then, the disorder which is in this man born of Adam, is voluntary, not by his will, but by the will of his first parent, who, by the movement of generation, moves all who originate from him, even as the soul’s will moves all the members to their actions. Hence the sin which is thus transmitted by the first parent to his descendants is called “original,” just as the sin which flows from the soul into the bodily members is called “actual.” And just as the actual sin that is committed by a member of the body, is not the sin of that member, except inasmuch as that member is a part of the man, for which reason it is called a “human sin”; so original sin is not the sin of this person, except inasmuch as this person receives his nature from his first parent, for which reason it is called the “sin of nature,” according to Ephesians 2:3: “We . . . were by nature children of wrath.” (ST, Part I-II, Q. 81, art. 1).
A few other quick points. The gift of original holiness and justice which God conferred on Adam and Eve was meant to be passed on to their posterity if they had not sinned. Would anybody consider this an injustice of God or rather a fact of God’s benevolence. Just as original justice and holiness was to be transmitted to the posterity of our first parents so was the disorder and the lack of the supernatural gift of original holiness and justice. Adam and Eve could not pass on to us their children what they themselves did not possess and by their sin they forfeited the supernatural gift of original holiness and justice, sanctifying grace, immortality, etc. It is just a fact of reality that you cannot give what you do not possess. We inherit from our parents our human nature and even some physical qualities such as the son looking very much like the father. We can even inherit from our parents external possessions such as they might leave to their children in wills. But we don’t inherit anything whether of nature or externally what they do not possess or cannot give.
We may also consider the revealed doctrine of the Mystical Body of Christ which is like the reverse side of how all men are implicated in Christ’s justice as all men are implicated in Adam’s sin (cf. CCC#404 and Romans 5). Thus, the explanation which I quoted from St Thomas above is scriptural, it stems from the teaching of St Paul and other scriptural sources such as the scriptural teaching of the unity of the human race in which the whole human race is derived from one ancestor, namely, Adam from whom even the first woman, Eve, came from (God formed Eve from the rib or side of Adam). Most likely, the doctrine of the Mystical Body of Christ was in the mind of St Thomas in the explanation of the transmission of original sin quoted above. Through the sacraments of the Church, Christ applies to us what he himself merited and gained for us by his passion, crucifixtion, and death and we are incorporated as members of his body. We, ourselves did not make atonement to God for our sins, Christ did this for us and we inherit from him through the sacraments what he himself did for us. Again by analogy, just as the members of a man’s body can share in the sin of a man, so also can they share in the good done by the man.
Accordingly, through baptism we are incorporated as members of Christ’s mystic body and we consequently share in what Christ did for us just as an alms given by the hand though moved by the will shares in the good of the man since the hand is a part of the man.