is the love of God.

_I answer that,_ As stated above (Q. 16, A. 1; I-II, Q. 99, A. 1), a
precept implies the notion of something due. Hence a thing is a
matter of precept, in so far as it is something due. Now a thing is
due in two ways, for its own sake, and for the sake of something
else. In every affair, it is the end that is due for its own sake,
because it has the character of a good for its own sake: while that
which is directed to the end is due for the sake of something else:
thus for a physician, it is due for its own sake, that he should
heal, while it is due for the sake of something else that he should
give a medicine in order to heal. Now the end of the spiritual life
is that man be united to God, and this union is effected by charity,
while all things pertaining to the spiritual life are ordained to
this union, as to their end. Hence the Apostle says (1 Tim. 1:5):
"The end of the commandment is charity from a pure heart, and a good
conscience, and an unfeigned faith." For all the virtues, about whose
acts the precepts are given, are directed either to the freeing of
the heart from the whirl of the passions--such are the virtues that
regulate the passions--or at least to the possession of a good
conscience--such are the virtues that regulate operations--or to the
having of a right faith--such are those which pertain to the worship
of God: and these three things are required of man that he may love
God. For an impure heart is withdrawn from loving God, on account of
the passion that inclines it to earthly things; an evil conscience
gives man a horror for God's justice, through fear of His
punishments; and an untrue faith draws man's affections to an untrue
representation of God, and separates him from the truth of God. Now
in every genus that which is for its own sake takes precedence of
that which is for the sake of another, wherefore the greatest precept
is that of charity, as stated in Matt. 22:39.

Reply Obj. 1: As stated above (I-II, Q. 100, A. 10) when we were
treating of the commandments, the mode of love does not come under
those precepts which are about the other acts of virtue: for
instance, this precept, "Honor thy father and thy mother," does not
prescribe that this should be done out of charity. The act of love
does, however, fall under special precepts.

Reply Obj. 2: The obligation of a precept is not opposed to liberty,
except in one whose mind is averted from that which is prescribed, as