Purity starts with the heart. There's a reason why when we are asked to pray "the prayer" to accept Christ that we are asked to "ask Christ into our heart." If you have ever heard of the salvation bracelet, you know the first color is black. Black represents our sin. We are all sinners. We all need to be cleansed.
Psalm 51:10 says, "Create in me a clean heart, O God, and renew a right spirit within me." How do we get this clean heart? Do we try to stop sinning? Well, that's a start. But we cannot cleanse ourselves. It's like when something sticky gets on the floor. We try to clean it with just water and soap, but it doesn't work. Sometimes we need something stronger, like goo be gone to clean it.
Jesus' blood is our sin be gone. When we accept him in our heart and ask him to forgive our sins, he does it. We are clean. We are white as snow. We are pure! Does that mean we should keep sinning? No, Romans 6:1-2 says, "What shall we say then? Are we to continue in sin that grace may abound? By no means! How can we who died to sin still live in it?" That's where purity in the heart comes in. We are to grow in God. We are to try to follow him. That means we are to try to stop sinning.
Matthew 5:8 says, "Blessed are the pure in heart, for they shall see God." I don't know about you, but I want to see God. I want my heart to be pure. I want my motives and desires to be God's motives and desires. I want his will to be done. We should all, as Christians, be at the point where we want to reflect God's glory so much so that he is seen in us. That when people look at us, they don't see us so much as they see God. Not in an idol like way but like in a, "you needed water, and I gave it to you, but it was God giving it to you through me." We don't deserve the glory. He does.
So, are you pure in heart? How can you follow God each day? How are you reflecting His glory?