The new wine is an illustration that Jesus gives. The Pharisees, along with the disciples of John the Baptist, can't understand why Jesus and His disciples are not adhering to the same rituals, like fasting and Sabbath observance, that they do. Jesus answers in Luke 5:34-39 and says, "I am bringing a new spiritual walk with God. I am not rejuvenating Judaism. I am making a break and introducing a whole new walk with God." What we have as Christians is deeply, foundationally different than any man or woman in the Old Testament. Yes, there will be saved people in heaven from the old covenant, but what Jesus brought is so different that the old and new cannot be put together. It's new wine.