Thomas Aquinas (ST I-II, q. 100, art. 5) compares the role of law in human communities with the role of divine law in the commonwealth of men under God: “just as the precepts of human law direct man in his relations to the human community, so the precepts of the Divine law direct man in his relations to a community or commonwealth of men under God.”

In each realm, two things are necessary: each member of the community must behave properly toward the head of the community, and each must behave rightly in relation to his fellows, other members of the community. Thus the Decalogue can be divided into two sections, which correspond with the two great commandments of Jesus: “It is . . . necessary that the Divine law should contain in the first place precepts ordering man in his relations to God; and in the second place, other precepts ordering man in his relations to other men who are his neighbors and live with him under God.”

From this binary division, he begins to subdivide the two sets of precepts. Right behavior toward the head of a community requires fidelity, reverence, and service. These match the first three commandments, which in Thomas’s counting are: 1) No other gods/no images; 2) bear Name; 3) keep Sabbath.

The seven other commandments lay out how each member should order himself toward other members. There are two types of relation to other members: To some we have particular relations (of kin, for instance), but to others we have general relations (common membership in the community).

Thomas puts it this way: “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.”

The final six commandments (from “do not kill” to two commandments against coveting) deal with harms to the neighbor’s person (do not kill), to someone united to him (do not commit adultery), to his possessions (do not steal), or to his reputation (do not bear false witness). The final six can also be divided triadically as sins of deed, of word, and of thought.

That triad, Thomas says, applies also to the first three commandments: The forbidden deed is making an image, the forbidden word is taking the Lord’s name in vain, the forbidden thought is a failed to remember Sabbath.

Schematically, Thomas offers this neat sketch of the organizing logic of the Decalogue:

Relation to Head----- Fidelity

                                    Reverence

                                    Service

Relation to Members---

Particular -- Honor Parents

General---- Harm to person of neighbor       }

   Harm to one united to neighbor     }  Deed

  Harm to neighbor’s possessions      }

  Harm to neighbor’s reputation           Word

Coveting neighbor’s things               Thought

I don’t agree with Thomas’s Augustinian numbering of the Ten Commandments, and I differ on the force of certain particular commandments. Still, I have to admit that this is pretty nifty.