i, 10) that "man is in
the Son of God, more than the Son in the Father." But the Son is in
the Father by unity of essence, and man is in the Son by the union of
the Incarnation. Therefore the union of the Incarnation is greater
than the unity of the Divine Essence, which nevertheless is the
greatest union; and thus the union of the Incarnation implies the
greatest unity.

_I answer that,_ Union implies the joining of several in some one
thing. Therefore the union of the Incarnation may be taken in two
ways: first, in regard to the things united; secondly, in regard to
that in which they are united. And in this regard this union has a
pre-eminence over other unions; for the unity of the Divine Person,
in which the two natures are united, is the greatest. But it has no
pre-eminence in regard to the things united.

Reply Obj. 1: The unity of the Divine Person is greater than
numerical unity, which is the principle of number. For the unity of a
Divine Person is an uncreated and self-subsisting unity, not received
into another by participation. Also, it is complete in itself, having
in itself whatever pertains to the nature of unity; and therefore it
is not compatible with the nature of a part, as in numerical unity,
which is a part of number, and which is shared in by the things
numbered. And hence in this respect the union of the Incarnation is
higher than numerical unity by reason of the unity of the Divine
Person, and not by reason of the human nature, which is not the unity
of the Divine Person, but is united to it.

Reply Obj. 2: This reason regards the things united, and not the
Person in Whom the union takes place.

Reply Obj. 3: The unity of the Divine Person is greater than the
unity of person and nature in us; and hence the union of the
Incarnation is greater than the union of soul and body in us.

And because what is urged in the argument "on the contrary" rests
upon what is untrue--namely, that the union of the Incarnation is
greater than the unity of the Divine Persons in Essence--we must say
to the authority of Augustine that the human nature is not more in
the Son of God than the Son of God in the Father, but much less. But
the man in some respects is more in the Son than the Son in the
Father--namely, inasmuch as the same suppositum is signified when I
say "man," meaning Christ, and when I say "Son of God"; whereas it is
not the same suppositum of Father and Son.
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TENTH ARTI