John 13:13
“You call Me Lord and Master, and you say well, for so I am.”
“You call Me.” He takes to Him their judgment, and then that the words may not be thought to be words of their kindness, He adds, “for so I am.” By introducing a saying of theirs, He makes it not offensive, and by confirming it Himself when introduced from them, unsuspected. “For so I am,” He says. Do you see how when He converses with the disciples, He speaks revealing more what belongs unto Himself? As He says, “Call no man master on earth, for One is your guide”, so also, “And call no man father upon earth.” But the “one” and “one” is spoken not of the Father only, but of Himself also. For had He spoken excluding Himself, how says He, “That ye may become the children of the light”? And again, if He called the Father only, “Master,” how says He, “For so I am”; and again, “For one is your Guide, even Christ”?
Source: Homilies on the Gospel of John (New Advent)