If we imagine a small house church in one of the cities of the eastern Mediterranean at the end of the first century, say Antioch, and if we imagine that it had just received a precious copy of Matthew's gospel, which was being read to the members for the first time—if we imagine such a situation, we can begin to get a sense of how that little house church must have heard this passage. Everyone was a new Christian. They have depended for their understanding of their new faith mostly on word of mouth including oral stories and snippets of instruction passed around among Christians. Maybe they had received (and passed on) a copy of one of Paul's letters, which also circulated among the churches; and just maybe they had received (and kept?) a copy of Mark's gospel, which was written a decade or two prior to Matthew's. Maybe. Or maybe not. Christian literature was scarce and at a premium, which meant that this church heard the Gospel of Matthew for the first time with keen interest. It brought things to light.
The story of Jesus' calling his first disciples must have be heard with particular interest. It was about them. It connected them to Jesus. It helped them understand how the whole "Jesus Movement" got its start and how the first generation of its leaders attained their positions of preeminence in the movement—particularly Peter who the story has being the very first disciple called by Jesus. They were a small congregation composed of mostly common folk who lived a hand to mouth existence. The story of Jesus calling the first members of the movement, who were also working class people, had to have been enlightening, precious, and a source of pride. In the world's eyes, we're nobodies; but in God's eyes, we are followers of his child, Jesus.
The story also reinforced the sense that as members of the movement they had a responsibility to share the Jesus story with family members, friends, and neighbors. Jesus called them to fish for other followers, just as he had called the first disciples to that holy calling. This explained why the sign of the fish, easy to draw, was the symbol of the movement.
After 1900 years or so of hearing this gospel read and, in recent centuries, reading it for ourselves, it is all but impossible for us to capture the way its first auditors must have heard it all those centuries ago. But, we can at least sense the profound impact it would have had on many of them, giving them both a sense of identity as Jesus' followers and a sense of purpose in sharing the good news about him with people they cared about. They and we owe a huge debt of thanks to whoever it was that thought up the idea of gospels, an amazingly important literary development in the life of the earliest church.