2 Thess. 1:5 reads:
...Ostensionem iusti iudicii Dei: ut digni habeamini regno Dei, pro quo et patimini.
...Which is a manifest token of the righteous judgment of God, that ye may be counted worthy of the kingdom of God, for which ye also suffer...
In commenting on the phrase 'a demonstration of the righteousness of God', Calvin refers to a remark of Ovid in the Amores:
Without mentioning the exposition given by others, I am of opinion that the true meaning is this — that the injuries and persecutions which innocent and pious persons endure from the wicked and abandoned, shew clearly, as in a mirror, that God will one day be the judge of the world. And this statement is quite at antipodes with that profane notion, which we are accustomed to entertain, whenever it goes well with the good and ill with the wicked. For we think that the world is under the regulation of mere chance, and we leave God no control. Hence it is that impiety and contempt take possession of men’s hearts, as Solomon speaks, (Ecclesiastes 9:3) for those that suffer anything undeservedly either throw the blame upon God, or do not think that he concerns himself as to the affairs of men. We hear what Ovid says, — “I am tempted to think that there are no gods.”
The footnote gives the reference:
“ Solicitor nullos esse putare deos .” — Ovid in. Am. 9:36. In order to see the appropriateness of the quotation, it is necessary to notice the connection of the words “ Cum rapiant mala fata bonos.... Solicitor ,” etc. ; — “When misfortunes overtake the good, I am tempted,” etc. — Ed
In addition, Calvin makes another 'classics reference' immediately after the passage
Nay more, David confesses (Psalm 73:1-12) that, because he saw things in so confused a state in the world, he had well-nigh lost his footing, as in a slippery place. On the other hand, the wicked become more insolent through occasion of prosperity, as if no punishment of their crimes awaited them; just as Dionysius, when making a prosperous voyage, boasted that the gods favored the sacrilegious. [The note explains thus: "Our author alludes to a saying of Dionysius the younger, tyrant of Sicily, on occasion of his plundering the temple of Proserpine."] In fine, when we see that the cruelty of the wicked against the innocent walks abroad with impunity, carnal sense concludes that there is no judgment of God, that there are no punishments of the wicked, that there is no reward of righteousness.