What is the significance (importance) of the title "The Merchant of Venice"?

Here is some insight for you:

There are two merchants in the play which immediately creates "confusion" or ambiguity.  There is Antonio, a merchant and friend of a man named Bassanio, and Shylock, a Jewish merchant. Either Antonio or Shylock might be the title character of the play, so from the start we don’t get a real sense of who the main character is. But what we do know is that ambiguity will be a central point of this play. Who does Shakespeare side with?  Does he take a side?  Who is his protagonist?