God... has shone in our hearts, to give the light of the knowledge of the glory of God in the face of Jesus Christ. (2 Corinthians 4:6)
The Letter to the Galatians really can be summed up in this way: a Christian is not one who does this and that and another thing which is prescribed to be done; a Christian is not one who refrains from doing this and that and another thing because they are forbidden; a Christian is not one at all who is governed by the externalities of a way of life, an order, a legalistic system which says, "You must," and "You must not," a Christian is comprehended in this saying, "It pleased God to reveal His Son in me" (Gal. 1:15-16). That is only another way of saying, "He opened my eyes to see Jesus," for the two things are the same. The Damascus road is the place. "Who art Thou, Lord?" "I am Jesus of Nazareth." "It pleased God to reveal His Son in me." That is one and the same thing.
Seeing in an inward way: that makes a Christian. "God... hath shined in our hearts, to give the light of the knowledge of the glory of God in the face of Jesus Christ" (2 Cor. 4:6). "In our hearts": Christ, so imparted and revealed within, is what makes a Christian, and a Christian will do or not do certain things, not at the dictates of any Christian law, any more than Jewish, but as led by the Spirit inwardly, by Christ in the heart. It is that that makes a Christian, and in that the foundation is laid for all the rest, right on to the consummation, because it is just going to be that growingly. So the foundation must be according to the superstructure; they are all of a piece. It is seeing, and it is seeing Christ.