...the prism through which all light concerning God is reflected is Jesus Christ. This means that Christology is the beginning and the end, better, the starting point and summary, of all Christian thought. Christology is Paul's theme when he writes, "For it is the very God who said. 'Let light shine out of darkness,' who has shone in our hearts to give the light of the knowledge of the glory of God in the face of Christ." (2 Cor 4:6)... Christology is the subject of theology. More precisely put, Jesus Christ is the subject of theology.
We Understand that God in any sense differentiated from Jesus Christ is unknowable. This needs to be affirmed from the start. John writes in the prologue to his Gospel, "No one has ever seen God; the only Son, who is in the bosom of the Father, he has made him known" (1:18). John repeats this idea forcefully in his first letter: "No one has ever seen God" (4:12)...Bible religion knows nothing about a God who can be found or made out from our side of things...Theology is unable to start in those places [first cause, ground of our being] because the picture of God that emerges from such beginnings is speculative...A theology that is Christology before it is anything else is a theology from the bottom up. It begins with the ministry of Jesus in his own time and space, and it states that it is entirely agnostic concerning anything other than what he has given us to know of the essential attributes of God...we begin, therefore, christologically, with a concrete historic figure
who appeared on the stage of human history...
Paul F.M. Zahl A Short Systematic Theology