In the next section of his Brief Admonition to the Polish Brothers, a work written against contemporary anti-Trinitarians, Calvin begins to deal with the different ways in which Scripture speaks of God. That is to say, Calvin makes the following traditional distinction: sometimes Scripture speaks of God simply, without reference to the Persons, and sometimes it speaks of the Persons in relation to one another.
The anti-Trinitarian mode of approach was often biblicist, and so Calvin begins right away by examining one of their proof-texts in relation to other parts of Scripture (and thus providing a handy illustration of how the analogy of Scripture works). (For another example of an exegetical attack against anti-Trinitarianism, see Zanchi’s De tribus Elohim.) (Also, there’s a hint at the autotheos in here, so the Calvin haters will want to make some popcorn.)
It is a false principle that is posited in the document, viz. that Scripture always speaks distinctly of the Father, the Son, and the Spirit, since it is clear from many passages that mention is made of God sometimes comparatively, sometimes without any distinction. If I maintain that there is a twofold way of speaking, that whole vain speculation that the Father of our Lord is the only and true God will soon disappear. To be sure, I profess that when mention is made of the Father and Son together, the Son is distinguished from the Father–but, lest the author of the document feel satisfied with himself, I deny that the distinction is absolute, as he ignorantly claims.
I shall begin from the first passage he shamefully corrupts: “I, Yahweh your God, am the one God” (Deut. 6.4). Here, since no comparison between the Persons is made, I say that the name of the one God is incorrectly restricted to the Father. For if the Father alone is Yahweh, who has his existence from himself, it will follow that the Son is not Yahweh. For how could that which is asserted of the Father alone be licitly transferred to the Son? Now, we must see whether Christ is Yahweh or not. Isaiah saw the God of Hosts sitting on his throne (6.1). It cannot be denied that this was one and the same Yahweh whom Moses proclaims to be the one God. But what of John? When Jesus had performed so many signs before them, they did not believe in him, in order that the word of Isaiah might be fulfilled. Next, consider this passage: “Isaiah said these things when he saw his glory and he spoke of him” (John 12.37). It is an empty cavil to stipulate that the glory of Christ was shown to the prophet because he is the image of the Father. Nor indeed will we be shaken from the opinion that, if Isaiah spoke of Christ, what he says of Yahweh is appropriate for Christ. 1