Vladimir Jankelevitch (Le Pur et l’Impur, 11) observes that we apply the concept of purity to wine and milk, defining the purity of beverages in opposition to admixture of other ingredients. In each case “purity” prohibits mixture, especially mixture of a thing with its supposed opposite.
Pure poetry is poetry without prose or didactic purpose. Pure music exists without reference to literature and without evoking visual scenes. Pure mathematics is mathematical speculation without any application or use. Pure language is a language without contamination of foreign words.
More abstractly, a thing is “pure” when it can be defined by itself, when it is self-identical (“identique a soi,” 13). When we can name a thing without reference to other things to which it is related, it is pure.
In these various senses, the God revealed in the gospel is an impure God. God is pure in the sense that He is wholly God, wholly independent of creation. God is pure in His utter, unadulterated goodness; He is light without shadow.
But, contrary to all early heresies, the Father is not defined only in his own terms, not defined only in Himself, but co-defined by the Son. The Son is Son of the Father; as Son, He cannot but be relative to a Father, who is the Father. In the gospel, the Father reveals Himself “impurely” in the Son and Spirit, who “contaminate” any sheer purism of the Father. And as if this were not enough, this impure God “pollutes” Himself further by uniting indissolubly to human nature. It was anticipated already in Torah, in which mixtures are holy, not polluted.
This is a great offense to purists of all ages – whether rationalists of the first or Pharisees of the twenty-first centuries. If God Himself is not “pure,” then can anything be pure in this sense? Isn’t the aspiration to purity exposed as a resistance to the impurity of the God of the gospel?
Trinitarian theology is thus a postmodernism beyond the imagination of postmoderns, for whom the purity of the ideal, the unreachable sublime beyond the veil, is a necessary limiting concept – the pure gift, pure justice, unconditional hospitality, pure speech. What Trinitarianism says is, on the contrary, that what lies beyond the veil has stepped out to show itself as light in all the splendid impurity of Source, Radiance, and Diffusion.