The real advance has obviously been made when we come to the INSTITUTIO of 1559, in which unio cum Christo [union with Christ] has become the common denominator under which Calvin tried to range his whole doctrine of the appropriation of the salvation achieved and revealed in Christ. For now in the Third Book, before he can speak of faith, of conversion and renewal, of the vita hominis christiani, of abnegatio nostri as its sum, of the necessary bearing of the cross, of the relation between this and the future life, then — and only then — of justification, of Christian freedom and prayer, of eternal election as the ulitmate presupposition of the whole, and finally of the future resurrection, according to the view attained in 1559 he has first to make it plain how it can come about at all that what God has done for us in Christ, as declared in the Second Book, can apply to us and be effective for us. The answer given in the noteworthy opening chapter of the Third Book is to the effect that it comes about through the arcana operatio Spiritus, which consists in the fact that Christ Himself, intead of being extra nos, outside the man separated from Him and therefore irrelevant to us, becomes ours and takes up His abode in us, we for our part being implanted into Him (Rom. 11:17) and putting Him on (Gal. 3:27). (Karl Barth CD 4.3.2, 550-51 cited by Charles Partee, The Theology of John Calvin, 195)