The need for purification?

Reading a book of mine (Brokenness and Blessing: Toward A Biblical Spirituality). Although only on chapter one, there was an image given about katharsis (purification). As Lent comes upon us, I would like to share it.

"Mary Douglas suggests a parable which brings out this point: the gardener removes weeds, so to 'purify' the flowerbeds; then she puts the weeds in the compost bin, and later restores them to the garden, since they have become life giving."

I know this is a rich metaphor and I do not want to taint it with my own interpretation, I just want to share and remember it for not only this Lent but all my seasons of katharsis to come...