To his neighbors a man behaves himself well both in particular and in general.  In particular, as to those to whom he is indebted, by paying his debts:  and in this sense is to be taken the commandment about honoring one’s parents.  In general, as to all men, by doing harm to none, either by deed, or by word, or by thought.  By deed, harm is done to one’s neighbor—­sometimes in his person, i.e. as to his personal existence; and this is forbidden by the words, “Thou shalt not kill”:  sometimes in a person united to him, as to the propagation of offspring; and this is prohibited by the words, “Thou shalt not commit adultery”:  sometimes in his possessions, which are directed to both the aforesaid; and with this regard to this it is said, “Thou shalt not steal.”  Harm done by word is forbidden when it is said, “Thou shalt not bear false witness against thy neighbor”:  harm done by thought is forbidden in the words, “Thou shalt not covet.”

The three precepts that direct man in his behavior towards God may also be differentiated in this same way.  For the first refers to deeds; wherefore it is said, “Thou shalt not make . . . a graven thing”:  the second, to words; wherefore it is said, “Thou shalt not take the name of the Lord thy God in vain”:  the third, to thoughts; because the sanctification of the Sabbath, as the subject of a moral precept, requires repose of the heart in God.  Or, according to Augustine (In Ps. 32:  Conc. 1), by the first commandment we reverence the unity of the First Principle; by the second, the Divine truth; by the third, His goodness whereby we are sanctified, and wherein we rest as in our last end.

Reply Obj. 1:  This objection may be answered in two ways.  First, because the precepts of the decalogue can be reduced to the precepts of charity.  Now there was need for man to receive a precept about loving God and his neighbor, because in this respect the natural law had become obscured on account of sin:  but not about the duty of loving oneself, because in this respect the natural law retained its vigor:  or again, because love of oneself is contained in the love of God and of one’s neighbor:  since true self-love consists in directing oneself to God.  And for this reason the decalogue includes those precepts only which refer to our neighbor and to God.

Secondly, it may be answered that the precepts of the decalogue are those which the people received from God immediately; wherefore it is written (Deut. 10:4):  “He wrote in the tables, according as He had written before, the ten words, which the Lord spoke to you.”  Hence the precepts of the decalogue need to be such as the people can understand at once.  Now a precept implies the notion of duty.  But it is easy for a man, especially for a believer, to understand that, of necessity, he owes certain duties to God and to his neighbor.  But that, in matters which regard himself and not another, man has, of necessity, certain duties to himself, is not so evident:  for, at the first glance, it seems that everyone is free in matters that concern himself.  And therefore the precepts which prohibit disorders of a man with regard to himself, reach the people through the instruction of men who are versed in such matters; and, consequently, they are not contained in the decalogue.