The title, The Winemaker, comes from a story in the Bible* about a wedding in Cana. Everyone is having a grand old time when the wine runs out. The story goes on to say that a man named Jesus tells the servants to fill waterpots with water, which he miraculously turns into wine. The details of this story are in the song The Winemaker.
From this point forward, Jesus is known as a sort of miracle man. Crowds follow him with the hope of witnessing these so-called miracles or perhaps with the hope of receiving one themselves.
As Jesus performs these miracles, he addresses many issues of social concern and resolves them, while chastising those who continue to keep them in existence. Thus, it seems fitting to name the story after him, even though he, himself, does not actually appear in the musical.
*Text Reference: John 2:1-11