All men were united in Adam. All were “one image” of God in Adam. “Adam is in us all.” We all sinned in Adam. Adam is saved and redeemed in us all. What does all this mean? It means simply, as St. Bernard says, that man’s creation in the image of God (ad imaginem) constituted all men as created “copies” of the Word Who is the eternal and uncreated Image of the Father. The potentiality in the human soul which makes man capable of being drawn to God is nothing else than a capacity to become more and more like the Word of God, and thus to participate in God’s own vision of Himself. St. Gregory of Nyssa says: “The whole of human nature, from the first man to the last, is but one image of Him Who is.” When Adam was created in the image and likeness of God, we all were created in him, with a nature capable of being conformed to the Word of God. Therefore Adam, who contains all human nature in himself, and is therefore “humanity,” is created in the image of the Image of God, Who has already decided, from all eternity, to become man in Jesus Christ. Hence in his very creation, Adam is a representation of Christ Who is to come, and we too, from the very moment we come into existence, are potential representations of Christ simply because we possess the human nature which was created in Him and was assumed by Him in the Incarnation, saved by Him on the Cross and glorified by Him in His Ascension.

Thomas Merton, The New Man (Kindle Locations 1203-1214). Macmillan. Kindle Edition.