The second chapter of the Westminster Confession of Faith is entitled “Of God, and of the Holy Trinity”. The statement consists of three articles, the first two of which expound that God is a “a most pure spirit, invisible, without body, parts, or passions” and that this God is “immutable, immense, eternal, incomprehensible”. After expouding these, and other classical themes regarding the attributes of God, there is a final section which briefly says that “In the unity of the Godhead there be three Persons of one substance, power, and eternity” and that the Father is unbegotton while the Son is begotten by the Father and the Spirit proceeds from the Father and Son.
This statement of faith is heretical from the title on. It assumes that God and the Trinity are two different things. And thus it goes on to say that the three persons subsist “in the unity of the Godhead”. This assumes that the unity of the Godhead itself is not constituted by the Three, but underlies them as some sort of “fourth”. Thus, the Westminster Confession posits a “god” behind and beneath the Holy Trinity which is modalism. Of course all this is to be expected when the opening two statments (by far longer) exposit all the real content of what we know about God in a manner totally independent of God’s revelation in Christ. In contrast, according to the Christian faith God is the Trinity and this is revealed through God’s action through Christ in the Spirit.
The Westminster Confession is theology at its worst. It is sub-Christian and posits a generic God as the “real” deity and then tries to tack on Jesus and the Trinity as an irrelevant afterword. Christian theology must repudiate statements such as this.