A sort of parenthesis begins here. Romans 2:16 refers back to the main subject of the paragraph, and not to the particular point on which the Apostle digresses in Romans 2:14-15, the virtual operation of law among the Gentiles as well as Jews.
By nature. — Spontaneously; of their own motion; not acting under the coercion of any external rule, but simply by the promptings of their own conscience left to itself.
The things contained in the law. — Literally, the things of the law. In this one instance the article is used, meaning, however, not “the law of Moses,” but “of this law,” or “of such law” — i.e., the ideal law spoken of just before.