which
impetrates sanctifying grace proceeds from some grace, as from a
gratuitous gift, since the very act of praying is "a gift of God," as
Augustine states (De Persever. xxiii).

Reply Obj. 2: Sometimes the merit of prayer regards chiefly something
distinct from the object of one's petition. For the chief object of
merit is beatitude, whereas the direct object of the petition of
prayer extends sometimes to certain other things, as stated above
(AA. 6, 7). Accordingly if this other thing that we ask for ourselves
be not useful for our beatitude, we do not merit it; and sometimes by
asking for and desiring such things we lose merit for instance if we
ask of God the accomplishment of some sin, which would be an impious
prayer. And sometimes it is not necessary for salvation, nor yet
manifestly contrary thereto; and then although he who prays may merit
eternal life by praying, yet he does not merit to obtain what he asks
for. Hence Augustine says (Liber. Sentent. Prosperi sent. ccxii): "He
who faithfully prays God for the necessaries of this life, is both
mercifully heard, and mercifully not heard. For the physician knows
better than the sick man what is good for the disease." For this
reason, too, Paul was not heard when he prayed for the removal of the
sting in his flesh, because this was not expedient. If, however, we
pray for something that is useful for our beatitude, through being
conducive to salvation, we merit it not only by praying, but also by
doing other good deeds: therefore without any doubt we receive what
we ask for, yet when we ought to receive it: "since certain things
are not denied us, but are deferred that they may be granted at a
suitable time," according to Augustine (Tract. cii in Joan.): and
again this may be hindered if we persevere not in asking for it.
Wherefore Basil says (De Constit. Monast. i): "The reason why
sometimes thou hast asked and not received, is because thou hast
asked amiss, either inconsistently, or lightly, or because thou hast
asked for what was not good for thee, or because thou hast ceased
asking." Since, however, a man cannot condignly merit eternal life
for another, as stated above (I-II, Q. 114, A. 6), it follows that
sometimes one cannot condignly merit for another things that pertain
to eternal life. For this reason we are not always heard when we pray
for others, as stated above (A. 7, ad 2, 3). Hence it is that four
conditions are laid down; namely, to ask--"for our