If any one saith, that man's free will moved and excited by God, by assenting to God exciting and calling, nowise co-operates towards disposing and preparing itself for obtaining the grace of Justification; that it cannot refuse its consent, if it would, but that, as something inanimate, it does nothing whatever and is merely passive; let him be anathema.
It seems to me that this is directed at least in part against the error of what some Protestants call monergism in our justification: the false notion that God requires nothing of a man with respect to his justification. While it is certainly true that God alone justifies us by his grace (as we have seen many times), and that we can do nothing to merit our justification, this is not the same as to suppose that we have nothing to do with respect to it whatsoever. God does not save us against our will. Justification is not something that the Lord does to us as though operating upon something inert.
There is a certain ineluctable sense in which even the Protestant error of "sola fide" necessarily operates in this same dogmatic atmosphere, because having faith – even on the Protestant's definition thereof – is a human act, and as such involves an act of the will. To deny this fact while at the same time insisting that we are saved "by faith alone" as though this having faith is not really a human act is flatly incoherent.