Read Matthew 5:17-20 and Psalm 72
The third office that Christ came to fulfill was that of king.
The Catechism explains that Christ carries out his office as king "by first subduing us to himself, ruling and defending us, and restraining and conquering all his and our enemies." Psalm 72 probably contains the most comprehensive Old Testament picture of Christ's subduing, ruling, and defending kingship.
There may be several aspects of his kingship which offend us. Most of us appreciate his restraining and conquering all his and our enemies. We all like to be defended. However, some of us may not appreciate the "subduing." Many of us like the Christmas card which says, "Wise men still seek him," because we think that we are the ones who were smart enough to seek him first. However, the Bible makes clear that he is the one who first chose us and in love subdued us. We would have never come to him otherwise. In fact, the Bible says that true hope and assurance come from knowing that he subdued us. One will never be assured by thinking he chose God, because he will forever be doubting whether it was sincere or will endure (cf. Ep. 1:18, "the hope of his calling"). To resent his subduing you is only to cut yourself off from comfort.
However, the most disappointing aspect of Christ's kingship to all of us at times is his ruling us. We do not like to be ruled by anyone, even a benevolent dictator. However, the Lord Christ demands allegiance from all.
It is only love that left heaven and came to earth to save us "while we were still sinners" that will enable us to rejoice at being subdued and ruled by Christ our king.
There is an interesting scene in the Old Testament where Joshua, who is on his way to conquer Jericho, encounters a man with a drawn sword. Not intimidated by any warrior, Joshua marches up to him and demands to know whose side he is on. The man, who turns out to be an angel, or perhaps even Christ, answers, "Neither. I am commander of the Lord's army." In other words, you never ask Christ whose side he is on. The question is only if you are on his side or not. Joshua responds in the right way—he falls down and worships. It is only by doing so that Joshua is in the position of experiencing the victory that God will bring over all of his enemies.
Everything in your life must come under his rule: your personal relationships, your thought patterns, the education of your children, and the way you spend your money.
So, what makes the righteousness of this allegiance surpass that of the Pharisees? In a word, it is love. If loyalty to Christ's kingship is only a matter of cold duty, it will never be joyful, and it will never endure. Joy and perseverance are the distinguishing qualities of true Kingdom service. It is only love that left heaven and came to earth to save us "while we were still sinners" (Ro. 5:8) that will enable us to rejoice at being subdued and ruled by Christ our king.