And Jesus said to them, “Can the sons of the wedding mourn while the bridegroom is with them? But days will come when the bridegroom is taken away from them, and then they also will fast.”
With these words Jesus explains that his presence for the disciples is like the presence of the bridegroom at a wedding, which is a time of joy and celebration. When the bridegroom—in this case Jesus—is with them, it is the time for joy and festivity, and therefore mourning or fasting is not necessary. But Jesus also makes it clear that a time will come when the “bridegroom,” that is, he himself, will be taken from them (a reference to his death, resurrection, and ascension), and then they will fast. This answer shows that fasting is connected to the right time and circumstances, and that the disciples will fast when it becomes necessary, that is, when Jesus is not physically with them.