Summary: Have you tried and tried to be holy only to fail time and time again? If so, then the liberating truth that you need is found in God's Name Jehovah-M’Kaddesh (Jehovah Who Sanctifies).
Purpose: To define holiness and its importance.
Aim: I want the listener to pursue holiness.
INTRODUCTION: One Sunday on their way home from church, a little girl turned to her mother and said, "Mommy, the preacher's sermon this morning confused me." The mother said, "Oh? Why is that?" The little girl replied, "Well, he said that God is bigger than we are. Is that true?" The mother replied, "Yes, that's true, honey." "And he also said that God lives in us? Is that true, mommy?" Again the mother replied, "Yes." "Well," said the little girl, "If God is bigger than us and he lives in us, wouldn't He show through?" 
God sanctifies us or makes us holy so that He can show through us.
For most Christians, though, "sanctify" or "holiness" are very puzzling words. We know that God is holy and that we should be holy, but we don't quite know what holiness is. We may even feel like it isn't very important because we also aren't sure how we can be holy.
What do you think when you hear the word "holy"? Do you think of an old lady with her grey hair tied up in a bun? Do you think of someone who talks using "thee's" and "thou's"? Do you think of someone who has no sense of humor? Is that your picture of holiness?
This morning we are going to let the Bible draw a picture of what real holiness looks like. Put aside what you think holiness is and let's see what the Bible says about holiness.
► I. What Does it Mean to be Holy?
The name Jehovah-M'Kaddesh, "The Eternally Self-Existent One Who Sanctifies"
probably describes the character of God more than any other name. The word SANCTIFY is essentially the same in the OT and the NT. "The word `sanctify' in the Old Testament frequently has the meaning of `setting apart'. It means the taking of something which was common before, which might legitimately have been put to ordinary uses, and setting it apart for God's service alone. It was then called sanctified or holy." 
There are two sides to holiness: a negative and a positive side.
► A. Be different from the world
1 Peter 1:14 As obedient children, do not be conformed to the former lusts which were yours in your ignorance, (NAU)
Leviticus 11:44--45 'For I am the LORD your God. Consecrate yourselves therefore, and be holy, for I am holy. And you shall not make yourselves unclean with any of the swarming things that swarm on the earth. 'For I am the LORD who brought you up from the land of Egypt to be your God; thus you shall be holy, for I am holy.' " (NAU)
1 Thessalonians 4:3 For this is the will of God, your sanctification; that is, that you abstain from sexual immorality; (NAU)
► B. Be like God
Isaiah 6:3 And one called out to another and said, "Holy, Holy, Holy, is the LORD of hosts, The whole earth is full of His glory." (NAU)
Revelation 4:8 And the four living creatures, each one of them having six wings, are full of eyes around and within; and day and night they do not cease to say, "HOLY, HOLY, HOLY is THE LORD GOD, THE ALMIGHTY, WHO WAS AND WHO IS AND WHO IS TO COME." (NAU)