Rules for a Right Understanding of the Ten Commandments

Psalm 119.96 teaches us that the scope of God's law is "exceeding broad": "I have seen an end of all perfection: but thy commandment is exceeding broad." Our Lord Jesus fleshes out what this means in the Sermon on the Mount by explaining that the Decalogue is not to be confined to the literal words which make up the ten commandments, but rather is to be understood as reflecting the full scope of spiritual perfection as comprehended in the moral law of God.

The Westminster Larger Catechism provides helpful guidance on how to understand the ten commandments aright (see the link for scripture references).

Westminster Larger Catechism:

Q99: What rules are to be observed for the right understanding of the ten commandments?

A99: For the right understanding of the ten commandments, these rules are to be observed:

1. That the law is perfect, and bindeth everyone to full conformity in the whole man unto the righteousness thereof, and unto entire obedience forever; so as to require the utmost perfection of every duty, and to forbid the least degree of every sin.

2. That it is spiritual, and so reaches the understanding, will, affections, and all other powers of the soul; as well as words, works, and gestures.

3. That one and the same thing, in divers respects, is required or forbidden in several commandments.

4. That as, where a duty is commanded, the contrary sin is forbidden; and, where a sin is forbidden, the contrary duty is commanded: so, where a promise is annexed, the contrary threatening is included; and, where a threatening is annexed, the contrary promise is included.

5. That what God forbids, is at no time to be done; What he commands, is always our duty; and yet every particular duty is not to be done at all times.

6. That under one sin or duty, all of the same kind are forbidden or commanded; together with all the causes, means, occasions, and appearances thereof, and provocations thereunto.

7. That what is forbidden or commanded to ourselves, we are bound, according to our places, to endeavor that it may be avoided or performed by others, according to the duty of their places.

8. That in what is commanded to others, we are bound, according to our places and callings, to be helpful to them; and to take heed of partaking with others in: What is forbidden them.

For comparison, see a briefer list of rules by an earlier Puritan, Richard Greenham:

Richard Greenham, A Short Forme of Catechising (1599 ed.):

Are there not some rules which serve for the better understanding of every one of the Commandements?

Yea, there be foure which have special uses.

1. First, in every Commandement where evill is forbidden, there the contrarie good is commanded.

2. Secondly, many moe evils are forbidden and many moe good things are commanded in every commandement, than in word are expressed.

3. Thirdly, because God is a Spirite, therefore his commandements are spirituall, and require spirituall obedience.

4. Fourthly, in every commandement where evill is forbidden, there the occasions of the evill is forbidden; & where good is commanded, there also the occasions of good are commanded.