What does Mark 2:19 mean?

Questioners—actually followers of John the Baptist (Matthew 9:14)— have asked Jesus' disciples why they don't fast, while the Pharisees and John the Baptist's disciples do. John's followers probably fast regularly in mourning and repentance for their sins and the sins of the nation. And, given that John is currently in prison, to petition God to secure his release.

Jesus obliquely explains that He is whom the Jewish people seek. According to Jesus, it is inappropriate to mourn in the presence of the Messiah. It is a time of celebration, similar to the week-long feasts held during a Jewish wedding.

The Messiah is not referred to as a groom in the Old Testament, but the metaphor of God as the husband of Israel is common, particularly in the book of Hosea. John the Baptist calls the Messiah the bridegroom in John 3:29.

It is only later, in retrospect, that Jesus's followers understand Him as the bridegroom to the church. Jesus will describe Himself as such in the parable of the ten virgins (Matthew 25:1–13). Paul will deepen the imagery in his letters (2 Corinthians 11:2; Ephesians 5:24–27). And the Apostle John will prophesy its fruition (Revelation 19:7–9).

John the Baptist's message of repentance is so strong it will reach Ephesus long before the Gospel does (Acts 19:1–5). This concept of repentance is important because it points to our need for a savior. In that context, fasting in mourning is an appropriate response. But once we have our Savior, we have reason to celebrate our new life. Shame is forsaken, and conviction is only a tool to bring us closer to God. Repentance is necessary, but it is momentary as Jesus restores us.