What does Mark 2:18 mean?Jewish scholars' interpretation of the Mosaic Law says God commands a yearly fast only once (Leviticus 16:29–31; 23:32): on the Day of Atonement (Yom Kippur). The passage says the Jews are to "afflict" themselves. "Afflict" is from the Hebrew root word anah which means "to oppress or humble." In the Hebrew, the word for "self" or "soul" was from the Hebrew root word nephesh, which means "life, creature, person, or desire." But in the old Hebrew, nephesh also meant "throat or appetite" (Isaiah 5:14). So the Jewish scholars interpreted "afflict yourself" as "humble your throat:" to fast from eating food.
Zechariah 7:3–5 and 8:19 suggest that the Jews observe corporate fasting four other times throughout the year. Tradition gives several dates. One is 17 Tammuz, to commemorate Moses breaking the two tablets as well as several events around the fall of Jerusalem to the Babylonians. The ninth day of Av (or Ab) as a memorial for the fall of the first and second temple. The third day of Tishrei is remembered in mourning for the assassination of Gedaliah, the governor of Judah under Nebuchadnezzar (2 Kings 25:22–26). The thirteenth day of Adar is noted in commemoration of the fast Esther called the Jews to observe while under threat by Haman (Esther 4:15–16).
In addition, Jews fast corporately as needed for mourning (Esther 4:3), in response to God's judgment (Joel 1:14), or to appeal to God (Judges 20:26; 1 Samuel 7:5–6; Isaiah 58; Jeremiah 14:11–12; Jonah 3:5), or to accompany a request (Ezra 8:21–23). Individually, Old Testament characters also fast in mourning (Nehemiah 1:4), to make requests to God (2 Samuel 12:16–17), for repentance (Daniel 9:3–19), and in times they needed wisdom (Esther 4:16).
John the Baptist is in prison at this point, but his followers apparently maintain some of his ascetic lifestyle. They might be fasting in mourning and repentance for Israel's sin and political situation or to ask God to release John. It is about them that Jesus gives the metaphor of the bridegroom.
After the second temple period, people start fasting as a way to show personal piety and discipline. The Pharisees fast for this reason, although they lose sight of the fact that piety excludes an audience (Matthew 6:16–18). The upcoming metaphors of the un-shrunken cloth and the new wine expose their flawed thinking.