what if nobody knows?

Matthew 6:16-18

And when you fast, do not look gloomy like the hypocrites, for they disfigure their faces that heir fasting may be seen by others. Truly, I say to you, they have received their reward. But when you fast, anoint your head and wash your face that your fasting may not be seen by others but by your father who is in secret. And your father who sees in secret will reward you.

Again, Jesus assumes that his followers will be fasting. fasting may be a neglected part of the Christian life at this point in history, but again Jesus points to the motivation as the problem for the hypocrites. they wanted others to see the sacrifice they were making. They wanted others to see their devotion. What about me? Am I fasting/serving/sacrificing because of God or because of others? How do I know? Would I be bothered if no one knew I was doing it?