Some of the disciples of John came to Jesus along with some Pharisees to ask about the truth about fasting. The practice of fasting was considered to be one of the three pillars of virtue in Jewish life. They came to Jesus and asked why His disciples were never seen fasting. Jesus gave them the answer that one day His disciples would fast, even though they were not doing it now. One time a church needed a major breakthrough so the pastor called the people to fast and pray and the following Sunday God moved in a wonderful way. Fasting is more than going without food, it is a spiritual principle of abstinence and denying oneself on behalf of seeing a breakthrough in an area of life or service. Jesus tells them there will be a time when His disciples will fast.
He is predicting His death on the cross. He is telling all Christians that a time of testing is coming upon them. Jesus teaches that the practice of fasting done by the Pharisees was more for show. Jesus wanted this practice to be one of the new man regenerated by the Holy Spirit. Jesus wants this practice to be preserved by His followers, but must be done in the right manner for the right reasons.