Jesus boldly proclaims in Matthew 5:17, "Do not think that I have come to abolish the Law or the Prophets. I have not come to abolish them but to fulfill them."
Jesus is going to accomplish them. He is going to put flesh on them bones.
Jesus expects the same from His listeners.
There are 2 choices:
You can either ignore parts of the law that aren't convenient to you
You can practice AND teach the whole thing.
Jesus loved to jab at the Pharisees. Here is one of first pokes at them. They are very righteous, but they were flawed. They would change the law to suit them, they would exalt the points of the law that were easy for them and they would do it all to try to get praise from other people.
Let's say you take a multiple-choice test with a fill-in-the-dot type answering sheet. What the Law does is provide you with the answer key. You can compare what you have done, with what is correct and judge yourself by that standard. You can even give yourself a score. Unfortunately (for us and them), the only score that is acceptable to God is 100%
Jesus comes in and says, "I'm not getting rid of the answer key. I'm going to explain to you what is right and why it is right and how to get to the right answer." Instead of learning that "b" is the wrong answer, you are going to learn what the right answer is and how to get to it. Jesus is going to write the problem on the board and step-by-step solve it for you.
Let's revisit the 2 choices I listed above:
Ignoring parts of the law would be like using that answer key to determine you've earned a score of 82%, then going back and crossing out the questions you got wrong or deciding that some of the ones you got right were worth double. You change the rules in your mind so that you can still get 100% and be right with God. This is only in your mind and God does not accept your scoring system. You can however probably convince a lot of human beings that you have succeeded in your venture to be righteous.
Practicing and teaching the whole thing implies a nice mix of knowing and doing.
Jesus is giving a tremendous pep talk to start this lesson:
YOU ARE BLESSED BY GOD
YOU ARE THE SALT OF THE EARTH
YOU CAN BE MORE RIGHTEOUS THAN THE PHARISEES!
The Son of God, who quickly establishes Himself as "one who teaches with authority" is actively pursuing the lost sheep of Israel. He is finding the people who have lost their way and feel beat down and thrown out. He is taking all of the people who have done poorly on life's exam and is telling them that He will be their tutor.
I believe that offer still stands today. For the lost sheep in the world, they need to see Jesus as their Great Shepherd. For those who are in Christ, how can we "live Jesus"? I think that comes down to what Jesus told the disciples much later in Matthew's gospel, "Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, and teaching them to obey everything I have commanded you."