As Jesus taught the people, most especially in Matthew 5-7 in the Sermon on the Mount, they were amazed. At the end of Matthew 7, it says that they were amazed because Jesus taught as one who had authority, unlike the way the teachers of the law taught them.
What does that mean, that he taught with authority? Let me give an example:
In Matthew 5, Jesus said, “You have heard that it was said to the people long ago, ‘You shall not murder, and anyone who murders will be subject to judgment.”
Of course, that is one of the 10 commandments. Commandment number 6: You shall not murder. Easy enough, makes complete sense.
However, Jesus then goes on to say something pretty radical. He says: But I tell you…
So, stop there for a second. Regardless of what comes next after “But I tell you”, Jesus has already gone too far, at least if he is just a man, but especially if he is just a prophet, or anything less than God himself. Why?
Because Jesus has just overridden God’s direct word to his people. God himself was the one who had given the commandments to Moses to give to the people. He was the one who spoke and told them “You shall not murder”, but now Jesus says, “But I tell you”.
See the problem?
If you are a Jew at that time, those four words, “But I tell you”, should have been absolutely shocking to you. Who does Jesus think he is to be able to tell us anything? Why does he think that he can change the word of God? You are going to change the commandments of God? Come on…
Yet that is exactly what Jesus did. In fact, he didn’t just do it once. He went on with regard to lust, divorce, taking oaths, love for others, prayer, fasting, and many other things. Jesus is, himself, giving direct commands, not simply pointing back to the commands of God as given in the time of Moses.
Now, let’s ask ourselves, why would he do that?
Jesus is, of course, trying to help the people understand the true heart behind each one of these different commands. If we return back to the question of murder, Jesus said that if anyone is angry with another person, they will be subject to judgment. He is trying to explain to the people that he wants their hearts. It is the condition of their hearts that makes the difference, not just the outward action. The law speaks to the actions and creates consequences for the actions, but the heart and reasoning behind the law is that God wants his people to live in love, to live in harmony, with one another. They should never even get to the point where they want to murder one another because their hearts are pure for one another. This is a way of living by the Spirit of God, not just by the letter of the law.
But I think that there is another reason as well. Jesus was not just teaching the people, but he was showing them who he was. By saying, “You have heard that it was said…” and then going on to say, “But I tell you…”, Jesus is showing himself. He is showing his true identity. He is showing who he truly is.
In what way?
A man cannot say “But I tell you…” over the words of God. Not possible. We should never even try.
But God himself can explain His intent behind His own words. And that is what Jesus is doing. He is teaching the people, but in the process Jesus is revealing his true identity. He is revealing that he is God Himself that has come here to the earth in the form of a man, in the form of Jesus.
So this is why, at the end of the Sermon on the Mount in chapter 7, we see Jesus say this:
Therefore everyone who hears these words of mine and puts them into practice is like a wise man who built his house on the rock. The rain came down, the streams rose, and the winds blew and beat against that house; yet it did not fall, because it had its foundation on the rock. But everyone who hears these words of mine and does not put them into practice is like a foolish man who built his house on sand. The rain came down, the streams rose, and the winds blew and beat against that house, and it fell with a great crash.
Matthew 7:24-27
Jesus tells the people that these are his words, yet the people recognize the authority with which Jesus is speaking. They understand that Jesus is giving commandments, not simply looking back to the commandments that were given and teaching them. That is good, but that is not what Jesus was doing.
So here we see the authority of Christ. The people who heard Jesus recognized that authority, and we must do the same, listening to what Jesus said and obeying him. In doing this we learn to walk by his Spirit, obeying his words, the words that will lead to eternal life.