Harmless as a dove, is Christ's interpretation of the beautiful emblem. And so the Spirit of God is purity itself. He cannot dwell in an unclean heart. He cannot abide in the natural mind. It was said of the anointing of old, "On man's flesh it shall not be poured."
The purity which the Holy Spirit brings is like the white and spotless little plant which grows up out of the heap of manure, or the black soil, without one grain of impurity adhering to its crystalline surface, spotless as an angel's wing.
So the Holy Spirit gives a purity of heart which gives its own protection, for it is essentially unlike the evil things which grow around it. It may be surrounded on every side with evil, but it is uncontaminated and pure because its very nature is essentially holy and divine. Like the plumage of the dove, it cannot be soiled, but comes forth from the miry pool unstained and unsullied by the dark waters, because it is protected by the oily covering which sheds off every defilement and makes it proof against the touch of every stain.