We purify water, air, coffee, oil, fuel, and all kinds of other liquids by running them through a filter. We cannot hope to remain morally pure in a world like this unless we have a filter. We cannot hope for our children to remain pure unless they have a filter. We can be their filter while they are very young, but every day as they get older they will see and hear more from this world, and they will be exposed to all of its filth and corruption. To maintain purity we must have something between us and the world around us that stops the filth before it goes in our eyes and ears.