By the Christological principle we understand the idea of an eternal union of God and man in the person of Christ as the medium of God’s self-communication and self-revelation to the world, and the consummation of all his ways and works. This implies on the one hand that Christ is the principle of the divine constitution of the world, and that in him, as St. Paul says, all things consist or hold together. He is not an accident or an afterthought in the divine world-plan, but its central and determinative idea, the real root as well as the culminating head of all things. It implies that Christ is the principle of all sound knowledge of God and of his ways and works. We can only know God aright in the light and inspiration of Christ. It follows, then, that the conception of love must be the determinative principle in any true or christian doctrine of God. No doctrine of God would be christian at all that is ruled by any other conception; as, for instance, the conception of sovereignty, of honor, or of glory.
William Rupp, The Reformed Quarterly, 1891, (p. 46).
And also:
But while the Holy Ghost is the agent in the work of regeneration, as above said, he is not the originator of the new life which he therefore communicates to the human soul. He does not create it ex nihilo just before planting it in the soul. The Spirit is not the author but the giver of life; and the life which he gives is that of Christ, the exalted and glorified God-man. Christ is the sole fountain of spiritual life for the whole human race. We must observe, however, that the new life thus lodged in man is not to be regarded as holding in separation from Christ after it has come to exist in the human soul. On the contrary it forms a perpetual bond of union between Christ and the soul’ so that the soul is in Christ as the branch is in the vine, or as the members of the human body are in the body, ‘Ye in me, and I in you.’
John Swander, The Mercersburg Theology (pg. 141-143).
