Theophylact of Ohrid

Although, it would seem, he says here the same thing, the inferences through comparison are different. Above he speaks of our sinfulness and then, adding that we have been justified, concludes through comparison: He who justified us sinners by His death will all the more save those who have been justified. But now, mentioning the death and life of Christ, he again reasons comparatively: when we were reconciled by the Blood and death of the Lord, how shall we not now be saved in His life? …

Commentary on Romans ↗

Thomas Aquinas

Then when he says, for if, when we were enemies, he shows the necessity of his conclusion, which proceeds by arguing from the lesser to the greater. And one should observe here two comparisons of lesser to greater, one on our part and one on the part of Christ. On our part he compares enemies to those who are reconciled. For it seems a lesser thing that someone should treat enemies well who are already reconciled. On the part of Christ he compares death to life. …

Commentary on Romans ↗

Bernard of Clairvaux

He was not returning love but freely offering it. For who had given him anything first, that it should be returned to him? "Not that we had loved him, but that he first loved us." He loved us even before we existed, and in addition he loved us when we resisted him. …

Sermons on the Song of Songs, Sermon 20 ↗