In the day when God shall judge the secrets of men by Jesus Christ according to my gospel.
In the day when, [the received reading, hote (G3753), is better than hee (G3588), which Lachmann adopts]
God shall judge the secrets of men (cf. Ecclesiastes 12:14; 1 Corinthians 4:5); here specially referring to the unfathomed depths of hypocrisy in the self-righteous, whom the apostle had to deal with.
By Jesus Christ according to my gospel - my teaching as a preacher of the Gospel (cf. Acts 17:31). This whole verse seems clearly to be the conclusion of the unfinished statement of Romans 2:12.
Expostulation with the Jew Resumed and Concluded (Romans 2:17-29)