The heart of God is inclined for the souls and he began by giving them an example of how fish should be caught and then teach them how to fish hearts.
Jesus taught them that where man gives up, that is where God begins to work and this is so that man does not take away God's glory.
Jesus showed them how with a net you could catch all the fish that you could, you would even have to ask for help to collect them from the net, the first thing he wanted to show them is that the net is to catch many fish and not some fish, because that the networks for that were designed.