The difficulty resolved: grace of justification taken widely and strictly
Thesis XXXIII. To solve this difficulty we must note that the Protestants use 'the grace of regeneration and justification' sometimes in a wider and sometimes in a stricter sense. In their usage, justification taken strictly and precisely is nothing but the absolution of a sinner for the sake of Christ's satisfaction, which is given and imputed to him. Understood in this way it is a benefit distinct from faith, the faith by which we share in it and which is therefore called justifying faith.
Taken more widely, though, the grace of justification includes the very faith by which we are justified. This is the sense the Protestants have in mind when they deny that any truly good works precede justification. For them, to come before justification is the same as to come before justifying faith, and nothing precedes justification that does not also precede faith.
So when they say that everything done before justification is sin and not a good work, they mean only that no good work can exist in a man before faith, and that all the works of unbelievers are sins.
Latin
XXXIII. Ad solvendam hanc difficultatem observandum est, apud Protestantes gratiam regenerationis & justificationis modo latius, modo strictius sumi. Ex Protestantium sensu, justificatio stricte & praecise accepta, non est aliud quam hominis peccatoris absolutio, propter Christi satisfactionem ipsi donatam atque imputatam, & sic concipitur ut beneficium distinctum a fide, per quam simus illius participes, & quae ideo fides justificans vocatur. Sub gratia vero justificationis, si latius sumatur, includitur ipsa fides per quam justificamur. Hoc sensu sumunt Protestantes justificationem, quum negant ulla opera vere bona illam antecedere. Idem enim cum ipsis est antecedere justificationem quod antecedere fidem justificantem. Nihilque eatenus justificationem praecedit, quod non fidem etiam praecedat. Adeoque quum dicunt omnia quae fiunt ante justificationem, non esse bona opera, sed peccata, non aliud sibi volunt, quam ante fidem nullum bonum opus in homine existere posse, sed omnia infidelium opera esse peccata.