When the new wine ferments and expands, it breaks the old skins because they can no longer stretch out. Jesus' audience would have understood the information about the wine's fermenting and expanding. (See: [[rc://en/ta/man/translate/figs-explicit]])
This metaphor contrasts the old teaching of the religious leaders against the new teaching of Jesus. The point is that people who are used to the old teaching are not willing to listen to the new things that Jesus is teaching. (See: [[rc://en/ta/man/translate/figs-metaphor]])