7 But why should we wonder that He rose from supper, and laid aside His garments, who, being in the form of God, made Himself of no reputation? And why should we wonder, if He girded Himself with a towel, who took upon Him the form of a servant, and was found in the likeness of a man? Why wonder, if He poured water into a basin wherewith to wash His disciples' feet, who poured His blood upon the earth to wash away the filth of their sins? Why wonder, if with the towel wherewith He was girded He wiped the feet He had washed, who with the very flesh that clothed Him laid a firm pathway for the footsteps of His evangelists?
In order, indeed, to gird Himself with the towel, He laid aside the garments He wore; but when He emptied Himself [of His divine glory] in order to assume the form of a servant, He laid not down what He had, but assumed that which He had not before. When about to be crucified, He was indeed stripped of His garments, and when dead was wrapped in linen clothes: and all that suffering of His is our purification. When, therefore, about to suffer the last extremities [of humiliation,] He here illustrated beforehand its friendly compliances; not only to those for whom He was about to endure death, but to him also who had resolved on betraying Him to death.
Because so great is the beneficence of human humility, that even the Divine Majesty was pleased to commend it by His own example; for proud man would have perished eternally, had he not been found by the lowly God. For the Son of man came to seek and to save that which was lost. And as he was lost by imitating the pride of the deceiver, let him now, when found, imitate the Redeemer's humility.
Source: Tractates on the Gospel of John (New Advent)