Chapter 8 of the Westminster Confession of Faith has two sections that
bear on this question. The first, section 2, is entirely orthodox:
Son of God, the second Person in the Trinity, being very and eternal
God, of one substance, and equal with the Father, did, when the
fullness of time was come, take upon him man’s nature, with all the
essential properties and common infirmities thereof; yet without sin:
being conceived by he power of the Holy Ghost, in the womb of the
Virgin Mary, of her substance. So that two whole, perfect, and distinct
natures, the Godhead and the manhood, were inseparably joined together
in one person, without conversion, composition, or confusion. Which
person is very God and very man, yet one Christ, the only Mediator
between God and man."
That’s the level of definition, though.
When it comes to applying this principle in a practical way, the WCF is
considerably less successful. Section 7 is a complete train wreck:
in the work of mediation, acteth according to both natures; by each
nature doing that which is proper to itself; yet by reason of the unity
of the person, that which is proper to one nature is sometimes, in
Scripture, attributed to the person denominated by the other nature."
to the semicolon, it makes sense and is orthodox. It even carefully
attributes the action to the Person "BY each nature" rather than to the
natures themselves. After the semicolon, though, it’s incoherent.
First, how can the unity of the person be introduced by the word "yet,"
as if it were a new consideration being introduced, when it is in fact
the basis of the statement just made? Second, how many persons do we
have here? The clause "attributed to the person denominated by the
other nature" sure makes it sound as if we have a person for each
nature. Third, if we assume that they couldn’t mean that (because it
would completely contradict what they’ve just said), we could make a
helpful edit and change that perplexing clause to "attributed to the
Person, as denominated by the other nature." But then the question
arises again, what the heck is "yet" doing introducing this sentence?
They would end up saying, "Even though the one Person acts by means of
both natures, Scripture sometimes attributes human qualities to that
Person while at the same time calling Him God." And that would be
complete nonsense, since the habit of Scripture they describe _depends
on_ the fact that the Person acts by means of both natures. In fact, if
the Person really is composed of two natures, there is no need to
explain it as a scriptural figure of speech when that one person is
called both man and God. So it doesn’t seem as if the WCF could mean
THAT either, but the only other option I see is to read it as teaching
two persons in Christ.