Blog 121: 3.11.5 - 3.11.8
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Is the Institutes a work of systematic theology? Yes and no. Calvin covers many of the topics of theology in his own inimitable way, but unevenly. There is much from the patristic and medieval theology that he takes for granted. His book is an occasional work, written to further the Reformation. It not written in the more timeless style of Hodge's Systematic Theology, say.
The Lutheran theologian Andreas Osiander (1498-1565) is largely forgotten now (he is best remembered, in fact, for being the author of the anonymous preface to Copernicus' De Revolutionibus Orbium Caelestium.) But he is also immortalised in the Institutes. Calvin was upset by his confusions over justification
For Calvin justification entails the imputation of Christ's righteousness. For Osiander, Christ's righteousness is literally the believer's, it becomes one of his properties. 'Christ's essence is mixed with our own", as Calvin puts it, and there are a number of reasons why this is unacceptable. As regards justification, it is a double error. Not only is it a confusion over how Christ's righteousness becomes the believer's, but it shows misunderstanding about the nature of the believer's union with Christ, which is a bond established by the Spirit, not a merging as envisaged by Osiander. For Calvin justification and sanctification are distinct but inseparable. But both become ours through the Spirit, as we are united to Christ. In merging Christ with the believer Osiander also confounds justification and sanctification: a serious blunder.
However, there is one point of agreement - faith itself does not justify, it is for Calvin (merely) 'a kind of vessel', the 'instrumental cause' of justification.