Actus humanus ex hoc quod est bonus vel malus, habeat rationem rectitudinis vel peccati, quia omnis actus voluntarius est malus per hoc quod recedit ab ordine rationis et legis aeternae, et omnis actus bonus concordat rationi et legi aeternae.
A human action has the formal aspect of rectitude or sin from the fact that it is either good or evil, because every voluntary action that turns aside from the order of formal aspect and of the Eternal Law, is evil, and every good action is in accord with formal aspect and the Eternal Law.
Unumquodque ordinatur ad finem per actum suum. Et ideo ratio peccati, quae consistit in deviatione ab ordine ad finem, proprie consistit in actu.
Each thing is ordained to its end by its action. And therefore the formal aspect of sin, which consists in straying from the order to the end, consists properly in an action.