John 13:12

12.When then he had washed their feet. Christ at length explains what was his intention in washing the feet of his disciples; for what he had said about the spiritual washing was a sort of digression from his main design. Had it not been for the opposition made by Peter, Christ would not have spoken on that subject. Now, therefore, he discloses the reason of what he had done; namely, that he who is the Master and Lord of all gave an example to be followed by all the godly, that none might grudge to descend to do a service to his brethren and equals, however mean and low that service might be. For the reason why the love of the brethren is despised is, that every man thinks more highly of himself than he ought, and despises almost every other person. Nor did he intend merely to inculcate modesty, but likewise to lay down this rule of brotherly love, that they should serve one another; for there is no brotherly love where there is not a voluntary subjection in assisting a neighbor.

Know you what I have done? We see that Christ, for a short time, concealed his intention from his disciples, but that, after having tried their obedience, he seasonably revealed to them that which it was not expedient for them previously to know. Nor does he now wait till they ask, but of his own accord anticipates them. The same thing will be experienced by us also, provided that we suffer ourselves to be guided by his hand, even through unknown ways.