Gibbs, Jeffrey A. “Matthew 6:16-18: Fasting." Matthew 1:1-11:1. St. Louis: Concordia Publishing House, 2006, pp. 348-350.
Gibbs observes that Jesus' purpose in his teaching on fasting, as earlier in Matthew 6 about charity and prayer, is likely to urge the disciples not to seek honor from humans but from God (Gibbs 2006, 349). They engage in the works, many of which can be known. Howeer, they reject the motive of being seen to be doing them.
Gibbs recognizes a strong emphasis on fasting in Judaism of this period. There was an assumption that a faithful person would fast. In Luther's practice as well, fasting was assumed to be perfectly normal. For Christians in the early 21st century i nNorth America, it is much less common (Gibbs 2006, 349). However, Gibbs suggests the development of such a habit of discipline can be of benefit for us as we learn to take control of our desires. It then generalizes into a disciplined life of, for instance, charity and prayer (Gibbs 2006, 350).