The second imperfection: the good acts themselves fall short
Thesis XIV. Second, the good acts themselves, considered in their own right, fall far short of the highest perfection, even in those who are as perfect as anyone can be in the state of this weak and mortal life.
We do not mean only that godly people, in doing good, fail to reach the perfection that the blessed in heaven attain. We mean that they also stop well below the degree of perfection that the law, strictly taken, requires of a human being, the degree to which humanity was bound by the law of its first creation.
Latin
XIV. Sed praeterea ipsi actus boni per se considerati, idque etiam in viris pro hujus vitae mortalis & infirmae statu maxime perfectis, multum tamen a summa perfectione deficiunt. Neque id tantum volumus pios homines in bene agendo non attingere perfectionem illam ad quam beatae mentes in coelo perveniunt: sed illos quoque multum subsistere infra perfectionis gradum quem lex rigide sumpta ab homine exigit, & ad quem homo ex prima creationis lege obligabatur.