"Blessed are the pure in heart, for they will see God" (Matthew 5:8).
Have you ever seen a tree that looks perfect on the outside, but when you cut it down, it is completely hollow on the inside? A tree like that is blighted, or diseased. Without its core, it cannot survive. The inside, where the sapwood is, provides the nourishment for the tree to continue growing strong and healthy. If it is hollow inside, a tree has no way to stay strong and healthy. No matter how good it looks on the outside, if it is rotten inside, it has no stability and no lasting life.
Each of us, every person who has ever lived, is born blighted. We are born as sinners and it doesn't take long to begin acting like sinners (Romans 5:12). We rebel against God, rejecting his perfect, pure standards (Romans 3:23). No one is pure on their own. Instead, each of us is imperfect and rotten (Romans 3:10-18). It doesn't take much to make us impure. James tells us that a person who sins in only one thing is guilty of breaking the entire law (James 2:10). We each were born like that tree that may look good on the outside but is rotten to the core. In reality, most of us have some of the rottenness showing on the outside, too.
Thank God there is a solution to our rotten condition. Jesus Christ is the answer to our rotten impurity. We need a righteousness from God (Romans 3:21-24). We don't have it in ourselves to be pure enough to please God. We need to be given the righteousness of Christ so that when God looks at us, he sees the perfection of Christ in us. When we turn to Christ in faith, we do not become perfect in everything we do. We still will sin. The difference is our core has been replaced! When God looks at us, instead of seeing a rotten core, He sees the perfection of his Son Jesus and accepts us because of Jesus in our life. We are justified - declared to be righteous before God. We become pure in heart and God sees us as pure children rather than rotten enemies. Because of Christ, we will see God (Matthew 5:8).
Once we are Christians, our core is pure because Jesus resides there (Colossians 1:27). Our standing is now perfect before God. But we continue to falter and sin. We still have our sinful flesh that pulls us away from God (Romans 7:22-23). The difference is now we have Christ in us to help us live purely.
We need to live out the reality of Christ in us. Christ has freed us from sin so we no longer have to obey sin. We can live righteously and press on toward living pure in heart (Romans 6:11-14). Sin is still present and active in our lives, but it does not have to control us. We now have Christ in us and the Spirit of God lives within us to provide us the strength to live purely (Romans 8:9). Our hearts belong to Christ. Live purely to reflect that.