Theophylact of Ohrid — on Rom 8:28 (Commentary on Romans)

“What was said before, namely: "the creation was subjected to vanity" (Rom. 8:20), also: "shall be delivered from the bondage of corruption" (Rom. 8:21), and further: "we do not know what we should pray for" (Rom. 8:26) — all of this, as we have noted, served as encouragement for those being persecuted in Rome. But what is now added is clearest of all. To those who love God, he says, all things, even those that seem unpleasant and grievous, work together for good. He did not say that no misfortunes befall those who love God, but that although they do befall them, God uses these misfortunes for the benefit of those who undergo them. Then, since this seemed incredible, he confirms it by the past, saying: "to those who are called according to His purpose." God, he says, called you when you were far away and made you His own: will He not all the more help the one who has been called? And a person becomes called "according to His purpose," that is, also according to his own free will. For the calling alone is not sufficient (because in that case all would have been saved, since all are called), but free will is also needed.”