NOTES for Mar 2:18-22
The original meaning of fasting in Yahwism and, consequently, in Judaism was associated with sadness, grief, misfortune, and mourning. Its most widespread form was fasting for the dead: after a person's death, relatives and friends would normally fast for at least one day, and often longer. Fasts were sometimes self-imposed not only by individuals but also by communities — religious communities or even entire cities — if, for example, they faced the threat of enemy invasion or a natural disaster such as an epidemic.
Later, contrition for one's own sins also became a reason to fast: a person was presumed to grieve over them as the greatest of misfortunes and therefore to fast. In the religious life of Gospel times, particularly among the Pharisees and the followers of John the Baptist, a practice of weekly fasting, usually twice a week, had developed. It was assumed that a person should spend these days in repentance.
As often happens, a spiritual practice that was beneficial at first degenerated over time into a pious religious custom, and a compulsory one at that. To appear before fellow believers on a fast day as someone who was not fasting, for example by being cheerful, laughing, or dressed festively, meant provoking at least bewilderment, if not condemnation, among those around. Hence the question to Jesus about His disciples, who did not observe the fasts. Jesus restores fasting to its original meaning: in the spiritual sense, fasting means above all the grief and anguish of being forsaken by God, when a person weeps not only over his sins but also because through them he has lost God and the possibility of communion with Him.
By speaking of Himself as the Bridegroom, an unmistakable allusion here to the wedding feast as the messianic banquet, the Saviour points to the meaninglessness of formal fasting when there is no genuine reason for it. As long as He is with His disciples, there can be no question of being forsaken by God and therefore no place for true fasting. The time will come when the disciples are left alone, and then their time to fast will come, but it will happen when it happens.