Summary: Waht it means to have a pure heart
Sermon on Mount
Blessed are the merciful
In the beatitudes, Jesus’ aim was to create a lifestyle in his followers that would make people think about the value of God, or to glorify God. The beatitudes start out showing us our great need for God and then the rest show us what it means to live like Jesus or walk in righteousness.
1. Jesus is concerned about my heart
This beatitude tells us that Jesus is not only concerned with our behavior. He wants to go deeper than the way we act - In the OT it was said not to commit adultery but Jesus say anyone who looks at a woman lustfully has committed adultery. I think we as the American church focuses so much on do’s and don’t to the neglect of the heart. As long as we look ok; everything is ok. But anything done without you’re your heart in it, that is a heart of faith, is done in vain. Listen to Jesus -"’These people honor me with their lips, but their hearts are far from me. 9 They worship me in vain (Matt 15:8-9 (quickview) ).
Matthew 23:25 (quickview)  "Woe to you, teachers of the law and Pharisees, you hypocrites! You clean the outside of the cup and dish, but inside they are full of greed and self-indulgence. 26 Blind Pharisee! First clean the inside of the cup and dish, and then the outside also will be clean.
Matthew 15:18 (quickview)  But the things that come out of the mouth come from the heart, and these make a man ’unclean.’ 19 For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false testimony, slander.
Jesus did not come just to change bad habits; he came to change bad hearts. The heart is the center of the entire personality - feeling, willling, thinking. The heart is what you are when you peel everything away like an onion and all you have is the center. It is what you are when no one is looking, your thoughts, feelings, affections. What do you think about when your mind is in neutral; where does your mind drift when you begin to daydream? That tells you what your heart is set on. He is concerned with the heart, it is not enough to clean up ones act on the outside and not deal with the inside (Mat 15:8-9). Our culture, the world deals with the outside, modify peoples behaviors. God is much more concerned with the heart.
Lets look at a close parallel to this beatitude to see what it means to be pure in pure heart.
Psalm 24:3 (quickview)  Who may ascend the hill of the LORD? Who may stand in his holy place? 4 He who has clean hands and a pure heart, who does not lift up his soul to an idol or swear by what is false. 5 He will receive blessing from the LORD and vindication from God his Savior. 6 Such is the generation of those who seek him, who seek your face, O God of Jacob.
You can see what David means by a "pure heart" in the phrases that follow it. A pure heart is a heart that has nothing to do with falsehood. It is truthful and free from deceitfulness. Deceit is what you do when you will two things, not one thing. You will to do one thing and you will that people think you are doing another. You will to feel one thing and you will that people think you are feeling another. That is impurity of heart. Purity of heart is to will one thing, namely, to "seek the face of the Lord" (verse 6). Ie kids, parents, husbands, wives, employees.