John the Baptist was arrested. Mark 6:17 tells us that Herod had him imprisoned for preaching about immorality in the palace, and then later has John executed. Immorality is not good in the leadership of a nation. That's not the main part of the section, but that's still a relevant lesson.
The passage under review deals with Jesus calling His first disciples. Matthew highlights that this ministry opening in Galilee was a fulfillment of Isaiah's prophecy that a great light would dawn on the people of that region. It's the first part of Isaiah 9, where we often jump ahead to "For unto us a child is born...."
It is worth taking note that Jesus begins by preaching. Note that 4:17 highlights the message of the Lord as one of repentance. While His preaching also involves grace and mercy, we cannot miss that the opening message of Jesus is to repent!
After beginning this preaching, Jesus calls specific men to Himself. These men will be His disciples, and they will be the opening leadership of the church. That will come in another few years, for now the call is simple: follow Jesus. Then we tend to make it complicated.
The next point in this section is the beginning of the Sermon on the Mount. Now, you can grab a handful of books and get different views about which "Mount" or whether Matthew condensed multiple sermons to a summary or whatever else may have happened, but taken at face value, this looks like one sermon from Jesus. It covers all sorts of topics, and really would not have taken that long to deliver.
It just takes a lifetime to begin to live out.