Step back and look at the whole verse as one unit. By now you may be thinking, I understand this, it is so simple, but I cannot do it. And you are right. None of us can keep it consistently. Imagine putting a waiter’s white towel over your arm at dawn as a reminder to serve all day, never demanding your own way, always taking the smaller portion and the harder task. How long would the towel stay white? By breakfast it is stained with impatience, by lunch with resentment, and by afternoon you may be serving on the outside while rehearsing complaints on the inside. The towel does not prove that service is impossible. It reveals that our hearts are not naturally humble.
That is precisely what Jesus intends. He is not lowering the standard until we can congratulate ourselves for reaching it. He is showing us the beautiful life we were created to live and then exposing our inability to produce it apart from him. His commands lead us away from self confidence and toward grace. And here is the gospel that holds all six days together: Jesus is the one who kept this rule perfectly. He picked up a towel and washed his disciples’ feet. He treated us the way he would want to be treated, and then he went to the cross and bore the punishment for sins he never committed, so that we might have life.
If you are in Christ, you do not keep this rule to earn a standing with God; you keep it because you already have one. Through his Spirit you now have the power and the standing to begin living this way, not by yourself but in dependence on him. And every day when you fall short, and you will, his mercies are new every morning. The white towel does not last long, but it can be washed again and again. That is the grace of the God who knew we would need it and provided it in his Son.