16 But because “the Word was made flesh, and dwelt among us,” by His very nativity he made an eye-salve to cleanse the eyes of our heart, and to enable us to see His majesty by means of His humility. Therefore “the Word was made flesh, and dwelt among us:” He healed our eyes; and what follows? “And we beheld His glory.” His glory can no one see unless healed by the humility of His flesh. Wherefore were we not able to see? Consider, then, dearly beloved, and see what I say.
There had dashed into man's eye, as it were, dust, earth; it had wounded the eye, and it could not see the light: that wounded eye is anointed; by earth it was wounded, and earth is applied to it for healing. For all eye-salves and medicines are derived from the earth alone. By dust you were blinded, and by dust you are healed: flesh, then, had wounded you, flesh heals you. The soul had become carnal by consenting to the affections of the flesh; thus had the eye of the heart been blinded.
“The Word was made flesh:” that Physician made for you an eye-salve. And as He thus came by flesh to extinguish the vices of the flesh, and by death to slay death; therefore did this take place in you, that, as “the Word became flesh,” you may be able to say, “And we beheld His glory.” What sort of glory? Such as He became as Son of man? That was His humility, not His glory. But to what is the sight of man brought when cured by means of flesh? “We beheld His glory, the glory as of the Only-begotten from the Father, full of grace and truth.”
Of grace and truth we shall speak more fully in another place in this same Gospel, if the Lord vouchsafe us opportunity. Let these things suffice for the present, and be ye edified in Christ: be ye comforted in faith, and watch in good works, and see that you do not depart from the wood by which you may cross the sea.
Source: Tractates on the Gospel of John (New Advent)