Karl Barth on the Trinity
The Bible lacks the express declaration that the Father, the Son, and the Holy Spirit are of equal essence and therefore in an equal sense God himself. And the other express declaration is also lacking, that God is God thus and only thus, i.e. as the Father, the Son, and the Holy Spirit. These two express declarations, which go beyond the witness of the Bible, are the twofold content of the Church doctrine of the Trinity” (Church Dogmatics, I.1.437).