A New Commandment

John records Christ washing the disciples' feet to illustrate His desire that they serve one another and thus fulfill the new commandment, which John says is really the old commandment (1 John 2:7, 8). It is new only in the sense that Jesus sacrifice for them will enable them to keep that Commandment (Phil. 2:13).
Our problem with keeping the new commandment is self, which must die if we are to obey His commandment. Peter was allowed to live out his self-confidence until fear caused him to deny Christ. Only after he died to self and be restored by Jesus (John 21) would Peter be able to obey Christ's commission.