This verse teaches an expansive view of how to become an integrated, peaceful being. Instead of hardening one's categories with dualistic absolutes, it is more wholesome to integrate 'apparent opposites' into a unified view, that one is a mixture of what a dualist culture would label good/bad, ugly/beautiful, and so on. It's ONLY when we allow each energy of yin and each energy of yang to co-exist one with the other, we achieve union, unity, and wholeness. Otherwise, we are at war with ourselves.