Two groups known for devotion to God fasted often, and Jesus' disciples did not. The question asks why Jesus' followers stood apart. Barnes says the Pharisees fasted "regularly twice a week, besides the great national days of fasting" (on Matthew 9:14). He adds that "it is probable that this question was put to him when John was in prison," while John's grieving disciples kept days of fasting. Gill notes that "used to fast" can be read "were fasting," "perhaps that very day, and so were the more displeased at this entertainment." If so, they were fasting while Jesus' disciples feasted, and the contrast was hard to miss.

Jesus answered with a question of His own: "Can the children of the bridechamber fast, while the bridegroom is with them?" (Mark 2:19). He gave the answer Himself: "as long as they have the bridegroom with them, they cannot fast." Then He added, "But the days will come, when the bridegroom shall be taken away from them, and then shall they fast in those days" (Mark 2:20). He finished with two pictures: new cloth sewn on an old garment, and new wine put into old bottles (Mark 2:21-22).

Mark's "used to fast" translates a Greek phrase made of "were" (ēsan) and "fasting" (nēsteuontes). It can describe a habit, or something going on at that moment, which is why the ESV says "were fasting." Barnes takes it as a habit, "Were accustomed often to fast," while Gill allows that they may have been fasting that very day.

The Gospels differ on who asked. Matthew says "the disciples of John" came (Matthew 9:14). Luke places the question right after the scribes and Pharisees complain about the feast, and adds that John's disciples "make prayers" (Luke 5:30, 33). Gill brings the accounts together: both John's disciples and the scribes and Pharisees came.

The question was about a practice, but Jesus turned it into a question about Himself. Fasting fits a time of sorrow and seeking. Jesus said that time had not yet come for His disciples, because the bridegroom was with them (Mark 2:19). How His followers lived depended on whether He was present.

Matthew Henry sums up the principle: "There is a time for all things." Jesus did not throw out fasting. He said a day would come when the bridegroom would be "taken away," and then His disciples would fast (Mark 2:20). Henry calls that "a proper time to sit as a widow, in solitude and fasting." The new life Jesus brought would not fit inside old forms, like new wine that bursts old bottles (Mark 2:22).