who assert that God is the soul of the highest heaven. Again, others
have said that God is the formal principle of all things; and this was
the theory of the Almaricians. The third error is that of David of
Dinant, who most absurdly taught that God was primary matter. Now all
these contain manifest untruth; since it is not possible for God to
enter into the composition of anything, either as a formal or a
material principle. First, because God is the first efficient cause.
Now the efficient cause is not identical numerically with the form of
the thing caused, but only specifically: for man begets man. But
primary matter can be neither numerically nor specifically identical
with an efficient cause; for the former is merely potential, while the
latter is actual. Secondly, because, since God is the first efficient
cause, to act belongs to Him primarily and essentially. But that which
enters into composition with anything does not act primarily and
essentially, but rather the composite so acts; for the hand does not
act, but the man by his hand; and, fire warms by its heat. Hence God
cannot be part of a compound. Thirdly, because no part of a compound
can be absolutely primal among beings--not even matter, nor form,
though they are the primal parts of every compound. For matter is
merely potential; and potentiality is absolutely posterior to
actuality, as is clear from the foregoing (Q. 3, A. 1): while a
form which is part of a compound is a participated form; and as that
which participates is posterior to that which is essential, so
likewise is that which is participated; as fire in ignited objects is
posterior to fire that is essentially such. Now it has been proved
that God is absolutely primal being (Q. 2, A. 3).

Reply Obj. 1: The Godhead is called the being of all things,
as their efficient and exemplar cause, but not as being their essence.