In the context of these verses Jesus has just responded to the Sadducees and the Pharisees who were trying to test Him. When He left them He traveled by boat to the other side of the sea and said to His disciples, "Watch and beware of the leven of the Pharisees and Sadducees."
In Matthew 15 Jesus dealt with Sadducees and Pharisees from Jerusalem. In Matthew 16:1-4 He dealt with some more Sadducees and Pharisees in Magadan. Now He gets in a boat and He leaves them and when they get there He warns his disciples, "Watch and be aware of the leaven of the Pharisees and Sadducees."
Let me make an observation. First, false teaching can be found everywhere. We have seen this in these two chapters. We cannot escape it. It will be wherever Jesus' disciples go. In fact, false teaching loves to come around to where God's people are. So even if it is not found initially it will make its way in over time.
Secondly, notice that Jesus tells them to beware and to be watchful; but He does not tell them to be intimidated, scared or isolationist. False teaching is everywhere and we cannot escape it; therefore, we are called to be prepared, watchful and alert.
In this text I would like you to notice that Jesus is bringing up again an issue for their own good. He is doing this by posing 5 questions. And this will result in the disciples understanding these things when He is done.
Questions can be a very powerful tool in the mouth of a teacher. Last week someone asked me a question and it really made me think long and hard about something that I had not considered before. In this case, Jesus asked questions for a few reasons.
First, Jesus uses a question to confront the faithlessness of a conversation that the disciples were having. Secondly, Jesus asks a question to confront the disciples failure to comprehend the deeper meanings of Jesus' words and actions. Jesus wants his disciples to think deeper than the Pharisees and Sadducees (16:2-3). They could see the obvious but they could not understand the real meaning. The apostles had to do better than this and so should we. The third and fourth questions confront the disciples failure to remember two of the greatest miracles that Jesus performed. One happened as recently as Matthew 14. We are also prone to seek something new (16:1-4) instead of remembering something we are already aware of. The fifth question directly confronts their failure to see His true teaching.
After these questions Jesus then simply says, "Beware of the leven of the Pharisees and Sadducees." And then we read these words, "Then they understood..." Understanding can be a long, uncomfortable process, but the fruits of it are so pleasant. In this case, the disciples were beginning to see the importance of error in the religious leaders teaching and manner of life. Therefore they would beware and watchful in these things.