What is purity? On the concrete side, the dictionary gives this definition: Consisted of itself only, unmixed (Harrap's Chamber 2005). It gives several other definitions which I won't mention all, but this one : freedom from contamination, pollution or unwholesome or intrusive elements.
If we take the first definition, there isn't any pure element in wilderness. It's all mixed up matters. Even precious metal or gemstones need to be treated artificially to become pure. Which mean that we only find purity in treated things.
Paradoxically, nature itself is considered a pure beauty when untouched by man, hence we see the second definition. A nature free from pollution, contamination and so on.
what about the spiritual purity? Still according to the dictionary, it is chasteness or innocence (same dictionary as above). The French dictionary add : devoid of all darkness.
Besides small children you will hardly find a pure human being. Jesus was, some will argue. But the bible, who attest it, is and was throughout history (by the Gnostic, the Orthodox, the Catharses, the protestants, etc.) contested for its validity, some accusing it to be just a bunch of propaganda. Jesus as been reduced to be a married man with children (why not? I like this idea, makes him more human to me, more accessible).
Buddha, another pure man actually preached the middle way, between good and evil. There are many others and I cannot discuss about them all.
We simply cannot be pure, because we are all made of light and shadow, whether we like it or not.
That being said, I think there is actually a way of becoming pure. First we have to acknowledge our dark side and once we do, we don't need to freak out about it. We also look at our positive side. Then, we merge them together to create a spiritual unity. This is a stage that will lead us to enlightenment. Once there, we can say, we are pure. The dark side cannot reach us, not because we resist it, but because we don't care about it. When it strikes us, we let it soak us, then we let it go.