Principal Fairbairn explains how the doctrine of headship, that humanity derives its condition from that representative man with whom it is union, is a source of comfort, even considered under the aspect of that guilt and pollution we partake of in Adam:

And though, like every other peculiar doctrine of the Gospel, it will always prove a stone of stumbling to the natural man, it will never fail to impart peace and comfort to the child of faith. Some degree of this he will derive from it, even by contemplating it in its darkest side by looking to the inheritance of evil which it has been the occasion of transmitting from Adam to the whole human race. For, humbling as is the light in which it presents the natural condition of man, it still serves to keep the soul possessed of just and elevated views of the goodness of God. That all are naturally smitten with the leprosy of a sore disease, is matter of painful experience, and cannot be denied without setting aside the plainest lessons of history. But how much deeper must have been the pain which the thought of this awakened, and how unspeakably more pregnant should it have appeared with fear and anxiety for the future, if the evil could have been traced to the operation of God, and had existed as an original and inherent element in the state and constitution of man ! It was a great relief to the wretched bosom of the pro digal, and was all, indeed, that remained to keep him from the blackness of despair, to know that it was not his father who sent him forth into the condition of a swine-herd, and bade him satisfy his hunger with the husks on which they fed; a truly consolatory thought, that these husks and that wretchedness were not emblems of his father. And can it be less comforting for the thoughtful mind, when awakening to the sad heritage of sin and death, under which humanity lies burdened, to know that this ascends no higher than the first parent of the human family, and that, as originally settled by God, the condition of mankind was in all respects “very good?” The evil is thus seen to have been not essential, but incidental ; a root of man’s planting, not of God’s; an intrusion into Heaven’s workmanship, which Heaven may again drive out.


Typology of Scripture
, V.1, P.2, C.1

Boethius explains this in his little tractate, The Trinity is One God not Three Gods:

But the Divine Substance is Form without matter, and is therefore One, and is its own essence. But other things are not simply their own essences, for each thing has its being from the things of which it is composed, that is, from its parts. It is This and That, i.e. it is the totality of its parts in conjunction; it is not This or That taken apart. Earthly man, for instance, since he consists of soul and body, is soul and body, not soul or body, separately; therefore he is not his own essence. That on the other hand which does not consist of This and That, but only of This, is really its own essence, and is altogether beautiful and stable because it is not grounded in any alien element.