faith ought to pray that they may understand, as Augustine says
(De Trin. xv, 27). Therefore the gift of understanding is not
necessary for salvation: and, consequently, is not in all who are in
a state of grace.

Obj. 3: Further, those things which are common to all who are in a
state of grace, are never withdrawn from them. Now the grace of
understanding and of the other gifts sometimes withdraws itself
profitably, for, at times, "when the mind is puffed up with
understanding sublime things, it becomes sluggish and dull in base
and vile things," as Gregory observes (Moral. ii, 49). Therefore the
gift of understanding is not in all who are in a state of grace.

_On the contrary,_ It is written (Ps. 81:5): "They have not known or
understood, they walk on in darkness." But no one who is in a state
of grace walks in darkness, according to John 8:12: "He that
followeth Me, walketh not in darkness." Therefore no one who is in a
state of grace is without the gift of understanding.

_I answer that,_ In all who are in a state of grace, there must needs
be rectitude of the will, since grace prepares man's will for good,
according to Augustine (Contra Julian. Pelag. iv, 3). Now the will
cannot be rightly directed to good, unless there be already some
knowledge of the truth, since the object of the will is good
understood, as stated in _De Anima_ iii, 7. Again, just as the Holy
Ghost directs man's will by the gift of charity, so as to move it
directly to some supernatural good; so also, by the gift of
understanding, He enlightens the human mind, so that it knows some
supernatural truth, to which the right will needs to tend.

Therefore, just as the gift of charity is in all of those who have
sanctifying grace, so also is the gift of understanding.

Reply Obj. 1: Some who have sanctifying grace may suffer dulness of
mind with regard to things that are not necessary for salvation; but
with regard to those that are necessary for salvation, they are
sufficiently instructed by the Holy Ghost, according to 1 John 2:27:
"His unction teacheth you of all things."

Reply Obj. 2: Although not all who have faith understand fully the
things that are proposed to be believed, yet they understand that
they ought to believe them, and that they ought nowise to deviate
from them.

Reply Obj. 3: With regard to things necessary for salvation, the gift
of understanding never withdraws from holy persons: but, in order
that they may have no in