II. The Incarnation was the only effective remedy to the fall
Let the righteous then rejoice in the Lord, and let the hearts of believers turn to God's praise, and the sons of men confess His wondrous acts; since in this work of God especially our humble estate realizes how highly its Maker values it: in that, after His great gift to mankind in making us after His image, He contributed far more largely to our restoration when the Lord Himself took on Him “the form of a slave.” For though all that the Creator expends upon His creature is part of one and the same Fatherly love, yet it is less wonderful than man should advance to divine things than that God should descend to humanity.
But unless the Almighty God did deign to do this, no kind of righteousness, no form of wisdom could rescue any one from the devil's bondage and from the depths of eternal death. For the condemnation that passes with sin from one upon all would remain, and our nature, corroded by its deadly wound, would discover no remedy, because it could not alter its state in its own strength. For the first man received the substance of flesh from the earth, and was quickened with a rational spirit by the in-breathing of his Creator, so that living after the image and likeness of his Maker, he might preserve the form of God's goodness and righteousness as in a bright mirror.
And, if he had perseveringly maintained this high dignity of his nature by observing the Law that was given him, his uncorrupt mind would have raised the character even of his earthly body to heavenly glory. But because in unhappy rashness he trusted the envious deceiver, and agreeing to his presumptuous counsels, preferred to forestall rather than to win the increase of honour that was in store for him, not only did that one man, but in him all that came after him also hear the verdict: “earth you are, and unto earth shall you go;” “as in the earthy,” therefore, “such are they also that are earthy,” and no one is immortal, because no one is heavenly.
Source: Sermons (New Advent)