Purity means clean, not mixed with any other thing or substance. We can understand this truth in the physical realm. All sickness and disease is caused by something in our body that is not supposed to be there. Contaminates, pollution, infection by germs, viruses, or bacteria result in sickness and even death. In the spiritual realm it is much the same. Unclean spirits are mentioned more than any other in the Bible. Wickedness, sin, and evil are contagious and when we gaze upon it with our eyes and ears something filthy enters our mind and heart. Until the people who are called Christians separate themselves from the filth of this world and all its sources things are going to continue to get worse. The work of God is suffering greatly because of the sin and immorality that is commonly found in the churches.