John 13:14 - Ellicott's Commentary On The Whole Bible

Ye ought also to wash one another’s feet. — The argument is à fortiori. If He had so humbled Himself as to do the work of a servant for them, much more ought they to humble themselves for each other. To make his words as striking as possible, they are prefaced by the emphatic I, and “Master and Lord” is repeated from the previous verse, but in the inverse order, to give special prominence to the word of greater dignity.