To Florus 2.212
Grace, however, is not conferred in the same way, repeatedly applied to each sin individually. Instead, poured in once, it wipes away many different crimes in a single concentrated action of its power. That is why he says, ‘From many offenses to justification’ (Romans 5:16): it leads human beings freed from many offenses to the glory of justification bestowed on them. Therefore he does not here mean Adam’s single sin, as you suppose. He uses the numbers one and many solely to praise grace: grace need not be repeated as often as each mortal person has sinned, as though individual baptisms could heal only individual sins.
Latin
Gratia autem non eodem confertur modo, ut peccatis aeque admota singulis crebro repetatur; sed infusa semel uno virtutis suae impetu atque compendio diversa et plurima delet crimina. Ideo ait: Ex multis delictis in iustificationem [n340] , id est ex multis delictis liberatos homines ad gloriam perducit iustificationis indultae. Non ergo hic unum Adae peccatum, ut suspicaris, intellegit, sed ad hoc solum numerum admovit unius et plurium, ut ad laudem gratiae respiceret, quia non quoties peccatum ab unoquoque mortalium fuerat, totiens etiam frequentaretur gratia, quasi baptismata singula nisi peccatis singulis non possint mederi.