Jesus taught that there are three eternal destinies:
• Least in the kingdom
• Great in the kingdom
• Never in the kingdom
In the rest of Matthew 5 Jesus taught how He fulfilled the law by going back to the motives of the heart - hatred, lust, and love. This has to do with the spirit of the law, not just the letter of the law. The spirit of the law is never less than the letter—it is always more. The Pharisees were living only the letter and would not make it into the kingdom. Others who relaxed the letter of the law would be least in the kingdom.
Christians today think that there are only two choices: keeping the letter and relaxing it. The United States abounds with legalists. It also abounds with relaxed doers and teachers. The choice between “not in the kingdom” and “least in the kingdom” seems a poor one to me.
There is a third option: “whoever keeps them and teaches others to do so.”
"You have heard that it was said: 'You shall not commit adultery.' I, however, say to you that anyone who looks at a woman with an impure intention has already committed adultery with her in his heart" (Matthew 5:27-28).
Being great in the kingdom means following the fulfilled law seriously, from the heart.
It is very easy to become a “relaxer” of the law. The majority of Christians do it. First we look at the letter of the law (e.g. “You shall not commit adultery.”) and say, “To observe that would be Old Testament legalism.” Then we look at the fulfilled law (“Anyone who looks at a woman with an impure intention has already committed adultery with her in his heart.”) and say, “That is nice, but it is idealism. If I tried to obey that I would be riddled with guilt constantly.” By relaxing both the letter of God’s law and the heart motive behind it, we leave the door wide open for violating the law in both thought and action. This is why an increasing number of Christians find themselves in serious sexual sin. The person who has been redeemed by the Lord Jesus should have no difficulty believing His teaching and getting power from Him to obey that teaching.