Purity is a choice. It is defined as the freedom from anything that debases, contaminates and pollutes. You have to choose to stay away from things that could defile you. The farther you move from what defiles you the closer you move to what defines you.
A farmer went to the market to sell among other things, the cottage cheese and apple butter he made on his farm. He carried them in two large tubs of which he ladled out each one into the smaller containers that he sold. One day when he got to the Market, he realized that he had forgotten one of the ladles. He had no choice but to use one ladle for both products. Before long the two products had gotten so mixed up that you could hardly tell the difference.
You see when the child of God loses their purity, they are no longer different and distinct from the world. You and I are created to be like "Him", Jesus that is. To be holy as He is holy. To be in the world but not of the world.Blessed are the pure in heart for they shall see God. Matt 5:8
Once you have moved away from things that can taint and pollute your life, your vision of God will be so much clearer. Don't let people and things contaminate you. Get rid of everything that prohibits you from living a life of loving Jesus. Oh how spiritually fortunate are those that stay pure. They will see God clearly!