There is the option of reading only the second part of today's gospel. I hope not many people have taken it. For one thing it would deny people the chance to hear again one of the most beautifully poetic passages in the Bible - 'Land of Zebulun! Land of Naphtali! Way of the sea on the far side of Jordan, Galilee of the nations!'. Reading only the second part also makes the call of the first apostles quite spooky, as if a complete stranger suddenly turned up at the lakeside, called them away from their work and their families, and 'immediately' (we have it twice in Matthew's account) they left everything and followed him. It is hardly credible, on a human level.
People speculate about the physical presence of Jesus, how he might have made himself compelling for these men so that they were ready to do this, or of some powerful impulse of the Holy Spirit moving their minds and hearts from within so that they knew that this was what they should do. But reading the first part of the gospel passage opens another possibility which makes the response of the disciples more reasonable, more credible.
'Hearing that John had been arrested': this is a key moment in the unfolding of the mission of Jesus. We know that he and John the Baptist came on the scene together and that the mission of each is intimately bound up with the mission of the other. The moment of John's arrest is a sign, a trigger, for Jesus and it is from this moment that his public ministry began. The final act of the drama, in which they are both key players, has now begun.
We know that Jesus attached himself to the movement of thought and action that surrounded John the Baptist. He came to John for baptism. It is not unreasonable to think that Peter, Andrew, James and John were also associated with that movement. The gospels do not say that they were but neither do they say that they were not. Let's imagine that Jesus had already met them, along with John the Baptist and that, like Mary, Simeon, Anna and others, they were people who looked for the salvation of Israel, people who looked for the coming of the Messiah. It is not unreasonable and it makes Jesus' return to Galilee, to seek out these men, a perfectly plausible course of action at a human level. He knew that something very significant had happened with the arrest of John. He knew that the time had come for the Messiah to begin his public work. He went to Galilee to call these men to be with him in his mission.
At the level of God's unfolding plan we also learn much by including the first part of the gospel reading. The passage it quotes from Isaiah is a messianic text, written centuries before Jesus, to comfort and console an oppressed people, to offer to the people of that region words of encouragement and the promise of light and joy. Matthew quotes it to teach us that the longer term promise implicit in this text - its Messianic significance - is fulfilled in the arrival of Jesus in the very same territory of Zebulum and Naphtali.
This fulfillment is for the chosen people who carry the promises of God for the world. So Jesus begins to preach in the synagogues. This fulfillment is for all people. So Jesus begins to preach in the streets, on the hilltops and from the boats. He is a teacher and healer, bringing light where there is darkness and joy where there is illness.
The first part of the gospel gives us the triggers, then, that help us to understand the second part. One trigger is the arrest of John: Jesus knows that now he must take the lead in announcing the kingdom. He comes to Galilee to find men to help him, perhaps men he had already met in the circle of the Baptist. The second trigger is the text from Isaiah which Matthew implies is the key to interpreting the beginning of Jesus' public ministry. (In this it functions in the same way as the text from Isaiah 61 which, Luke tells us, Jesus read in the synagogue at Nazareth.) We know that Isaiah 8-9 is a messianic text and here is the Messiah, the One bringing light and joy, the source of unity for Paul's divided communities, the founder of the new Israel (Zebulum and Naphtali), the Saviour of humankind (Galilee of the nations). He continues to call people to be with him in his mission.