“We thus identify three fundamental principles for theology: God is the essential foundation (principium essendi); Scripture is the external cognitive foundation (principium cognoscendi externum); and the Holy Spirit is the internal principle of knowing (principium cognoscendi internum). The foundations of theology are thus trinitarian: The Father, through the Son as Logos, imparts himself to his creatures in the Spirit.
“The archetypal knowledge of God in the divine consciousness; the ectypal knowledge of God granted in revelation and recorded in Holy Scripture; and the knowledge of God in the subject, insofar as it proceeds from revelation and enters into the human consciousness, are all three of them from God. It is God himself who discloses his self-knowledge, communicates it through revelation, and introduces it into human beings. And materially they are one as well, for it is one identical, pure, and genuine knowledge of God, which he has of himself, communicates in revelation, and introduces into the human consciousness.“
Source: Herman Bavinck, Reformed Dogmatics: Prolegomena
Jojo Agot 