When Paul says “they show,” he evidently means their conduct shows, which may be rendered as “by what they do they show” or “by their behavior they indicate.”

“The work of the Law” may be taken either in the sense of what the Law commands (see Jerusalem Bible, An American Translation*, Revised Standard Version), or with the meaning of “the effect of the Law” (New English Bible, Moffatt).

Written in their hearts may be rendered as “exists in their hearts” or “is found in their minds.”

Show that this is true basically means “give testimony as a witness” (see New English Bible “their conscience is called as witness” and An American Translation* “their consciences will testify for them”). Paul gives three evidences to indicate that the Gentiles are a law to themselves, though they do not possess the Mosaic Law: (1) their conduct (2) their consciences, and (3) their thoughts.

It is difficult in many languages to distinguish between “heart” and “conscience.” In some instances there may be a highly idiomatic expression for conscience—for example, “the little man that stands within” or “one’s innermost.” More frequently one must combine the concepts of both thought and heart—for example, “how they think in their hearts.”

The pronoun this in the phrase this is true must refer back to the fact that what the Law commands is written in their hearts. It may be necessary to make this explicit by translating: “what they think in their hearts shows that what the Law commands is written there.”

Their thoughts sometimes accuse them and sometimes defend them is a difficult clause in Greek, though most modern translations accept the same exegesis that the Good News Translation follows. The Greek of this clause is difficult because there is no expressed object of the verb accuse or defend. It is possible to render this as the King James Version does, “their thoughts the mean while accusing or else excusing one another”; but the question is whether Paul is speaking of a person’s thoughts sometimes accusing and sometimes defending himself, or whether he is thinking of a person’s thoughts sometimes accusing and sometimes defending someone else. In light of the rest of the verse, the former of these possibilities is probably better. Accuse and defend are expressed in some languages as direct discourse—for example, “sometimes their thoughts say, You did wrong, and sometimes their thoughts say, You did right.”

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on Paul’s Letter to the Romans. (UBS Handbook Series). New York: UBS, 1973. For this and other handbooks for translators see here .