There is, however, a good reason why the subject of union with Christ should not be co-ordinated with the other phases of the application of redemption with which we have dealt. That reason is that union with Christ is in itself a very broad and embracive subject. It is not simply a step in the application of redemption; when viewed, according to the teaching of Scripture, in its broader aspects it underlies every step of the application of redemption. Union with Christ is really the central truth of the whole doctrine of salvation not only in its application but also in its once-for-all accomplishment in the finished work of Christ. Indeed the whole process of salvation has its origin in one phase of union with Christ and salvation has in view the realization of other phases of union with Christ. This can be readily seen if we remember that brief expression which is so common in the New Testament, namely, “in Christ.” It is that which is meant by “in Christ” that we have in mind when we speak of “union with Christ.” It is quite apparent that the Scripture applies the expression “in Christ” to much more than the application of redemption. A certain aspect of union with Christ, it is true, belongs strictly to the application of redemption. With that we shall deal later. But we would not deal properly with the subject of union with Christ unless we set forth, first of all, its broader meaning. We would not be able to appreciate that which falls within the application of redemption if we did not relate it to that which is broader.

Murray, J. (1955). Redemption: Accomplished and Applied (pp. 161–162). Grand Rapids, MI; Cambridge, UK: William B. Eerdmans Publishing Company.