What does Luke 5:38 mean?

Jesus is explaining that the freedom of the gospel He offers is incompatible with the hide-bound traditions of then-contemporary Judaism. Jesus fulfilled the law of Moses and did not discourage His Jewish followers from following the Law. He did condemn traditions and interpretations which went beyond Scripture, when they were enforced by the Pharisees. In the context of the stories of Luke 5:27—6:11, Luke highlights four ways in which this applies: associating with sinners, fasting in mourning when God the Son is present, seeing to one's bodily needs on the Sabbath, and helping others on the Sabbath.

Jesus warns Pharisees who might want to incorporate some of the manifestations of the gospel into their rigid religion: they can't. Their legalistic religious traditions are as brittle as an old hide that has been used to age wine. If the new wine of Jesus' gospel were to be forced into their traditions, the expansive grace would burst the skin and they would both be ruined. To follow Jesus, a "fresh wineskin" is needed: a new religious expression of faithfulness to God we know as "the church."

The Jews in the coming church will take some time to understand this. First, they will realize that the half-Jewish Samaritans can accept the gospel (Acts 8:4–25). Then, that devout Gentiles should be welcomed (Acts 8:26–40; 10). A bit later, a mass of Gentiles previously unfamiliar with Judaism will join the church in Syrian Antioch (Acts 11:19–26). Finally, the leadership will have to figure out how to fully integrate Jews and Gentiles in worship together (Acts 15). This new message requires a new expression.