ultery or of fornication: because he took unto
himself one who was his by command of God, Who is the Author of the
institution of marriage.

Accordingly, therefore, the precepts of the decalogue, as to the
essence of justice which they contain, are unchangeable: but as to
any determination by application to individual actions--for instance,
that this or that be murder, theft or adultery, or not--in this point
they admit of change; sometimes by Divine authority alone, namely, in
such matters as are exclusively of Divine institution, as marriage
and the like; sometimes also by human authority, namely in such
matters as are subject to human jurisdiction: for in this respect men
stand in the place of God: and yet not in all respects.

Reply Obj. 4: This determination was an interpretation rather than a
dispensation. For a man is not taken to break the Sabbath, if he does
something necessary for human welfare; as Our Lord proves (Matt.
12:3, seqq.).
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NINTH ARTICLE [I-II, Q. 100, Art. 9]

Whether the Mode of Virtue Falls Under the Precept of the Law?

Objection 1: It would seem that the mode of virtue falls under the
precept of the law. For the mode of virtue is that deeds of justice
should be done justly, that deeds of fortitude should be done
bravely, and in like manner as to the other virtues. But it is
commanded (Deut. 26:20) that "thou shalt follow justly after that
which is just." Therefore the mode of virtue falls under the precept.

Obj. 2: Further, that which belongs to the intention of the lawgiver
comes chiefly under the precept. But the intention of the lawgiver is
directed chiefly to make men virtuous, as stated in _Ethic._ ii: and
it belongs to a virtuous man to act virtuously. Therefore the mode of
virtue falls under the precept.

Obj. 3: Further, the mode of virtue seems to consist properly in
working willingly and with pleasure. But this falls under a precept
of the Divine law, for it is written (Ps. 99:2): "Serve ye the Lord
with gladness"; and (2 Cor. 9:7): "Not with sadness or necessity: for
God loveth a cheerful giver"; whereupon the gloss says: "Whatever ye
do, do gladly; and then you will do it well; whereas if you do it
sorrowfully, it is done in thee, not by thee." Therefore the mode of
virtue falls under the precept of the law.

_On the contrary,_ No man can act as a virtuous man acts unless he
has the habit of virtue, as the Philosopher explains (Ethic. ii, 4;
v,