Cap. VI Arg. 8: first — perseverance from God's gift (Jer. 32:40; 2 Thess. 3:3), not bare free choice
Nothing here can be shaken. First: if persevering faith could be foreseen in those to whom God has not yet decreed perseverance, that great good would come from human choice, not God's gift. All Scripture protests — saints' perseverance flows from God's gift: I will put my fear in their heart, that they may not depart from me (Jer. 32:40); Faithful is God, who will establish you and keep you from evil (2 Thess. 3:3). Augustine, following Scripture, taught that the power and will to persevere is given by grace's largess to saints predestined into God's kingdom — and not to others. So Aquinas is right: God's loving will that someone have this good is why he has it before others (ST 1.23.4).
Latin
Nihil video in hoc argumento quod ullo modo possit labefactari aut in dubium vocari. Nam primo, si quis diceret fidem perseverantem posse in aliquibus praevideri quibus Deus hanc perseverantiam nondum decreverit donare, ille tantum bonum ab humano arbitrio, non a Divino munere arcesseret. At tota Scriptura reclamat, quae perseverantiam sanctorum ex dono Dei ostendit dimanare: Reverentiam mei indam animo ipsorum, ut non recedant a me, Jer. xxxii. 40. 2 Thess. iii. 3. Fidelis est Deus, qui stabiliet vos et tuebitur a malo. Et Augustinus secundum Scripturas clare docuit, hanc perseverandi possibilitatem et voluntatem Divinae gratiae largitate donari sanctis in regnum Dei praedestinatis, aliis non donari. Est ergo verissimum illud Aquinatis: Voluntas Dei qua vult hoc bonum alicui diligendo, est causa quod illud bonum ab eo prae aliis habeatur, Part. 1. qu. 23. art. 4.