καὶ εἶπεν αὐτοῖς ὁ Ἰησοῦς· δεῦτε ὀπίσω μου, καὶ ποιήσω ὑμᾶς γενέσθαι ἁλιεῖς ἀνθρώπων.
I do not care for fishing. While some find it to be a relaxing hobby, I find it to be boring and tedious. Maybe it’s because my dad never took me fishing or maybe it’s because I prefer to have my nose in a book. Whatever the reason, fishing is not for me. And hunting even less so!
Yet much of the world depends on fish and other seafood to sustain its growing population. In his book Collapse: How Societies Choose to Fail or Succeed, scientist and author Jared Diamond notes,
While seafood consumption is high and rising in the First World, it is even higher and rising faster elsewhere, e.g., having doubled in China within the last decade. Fish now account for 40% of all protein (of both plant and animal origin) consumed in the Third World and are the main animal protein source for over a billion Asians….As a result of our dependence on seafood, the sea provides jobs and income for 200,000,000 people around the world, and fishing is the most important basis of the economies of Iceland, Chile, and some other countries. (Diamond, 2005, 479)
Throughout much of human history, fishing has been an important task. If you lived near a body of water then you got much of your food supply from it. This is true today and it was true in first century Palestine.
With Him All the Way
The Gospel of Mark has a very simple structure. In broad terms, there are three major sections: a prologue or introduction (1:1-15), the public ministry of Jesus (1:16-8:26), and the journey to the cross (8:27-16:8). Within the first section we can see three major divisions: the authority of Jesus (1:16-3:12), the teachings of Jesus (3:13-6:6), and the mission of Jesus (6:7-8:26). Each division begins with a pericope concerning the disciples. Why is this?
To put it simply, one of Mark’s goals in writing his Gospel is to turn readers who may know about Jesus into disciples of Jesus. So in his Gospel the disciples are far from minor characters on the stage that is Jesus’ life. Rather, they are there from the beginning and are vital to the story. And by including them so early in the narrative, Mark is emphasizing that the disciples had been with Jesus all the way. 
“Left their father Zebedee”
But the pericope in Mark 1:16-20 is also intended to demonstrate that the proper response to Jesus’ call is immediate and unwavering commitment. When Jesus sees Simon and Andrew casting their nets into the sea, he calls to them and says, “Follow me, and I will make you become fishers of men.” (1:17) And what is their response? καὶ εὐθὺς ἀφέντες τὰ δίκτυα ἠκολούθησαν αὐτῷ – “And immediately they left their nets and followed him.” (1:18) If this isn’t surprising, it should be. Mark’s audience would have recognized that in dropping their nets to follow Jesus, Simon and Andrew were leaving behind their livelihood, their source of life. Yet they drop their nets and at the call of Jesus follow him.
But Simon and Andrew are not the only ones who abandon fishing to follow Jesus. As he goes a little farther, Jesus sees James and John, the sons of Zebedee, in their boats repairing their nets. The text says, “And immediately he called them, and they left their father Zebedee in the boat with the hired servants and followed him.” (1:20) This is surprising not only because fishing was their source of food but also because apparently Zebedee’s fishing business was doing well enough that he could afford to have τῶν μισθωτῶν, “hired servants.” Furthermore, James and John left their own father behind to follow this man from Galilee. This is astonishing.
Mark is highlighting for his readers that discipleship is costly. You may have to abandon your source of food. You may not have incredible financial success. You may have to leave behind family. But the one you are following is one who teaches with authority and casts out demons (1:21-28), who can heal those who have been sick with leprosy or paralyzed for life (1:40-2:12), and who is even able to raise the dead to life again. (5:35-43) Sure, along the way you may be lumped in with “tax collectors and sinners” (2:15-16) but Jesus said he wasn’t where the healthy were but where the sick were.
“I will make you become fishers of men,” Jesus told Simon and Andrew. And that is one of the purposes of Mark’s Gospel: to make his readers fishers of men.
 Though as Jesus faces his own death they scatter. This turn of events is intended to emphasize a theme in Mark’s Gospel that no one really understands who Jesus is, not even his disciples. They may have expected a triumphant king but got a crucified prophet.
Jared Diamond. Collapse: How Societies Choose to Fail or Succeed. New York, NY: Penguin Books, 2005.