Creation, and the justification of the unrighteous, though done by God alone, are not, properly speaking, miracles, because they are not of a nature to proceed from any other cause; so they do not occur outside the order of nature, since they do not belong to that order. [ST I, Q105, A7, ad 1]Can any clearer declaration of the facts be imagined? Justification is "done by God alone," and it is something that could not possibly have any other cause, by its very nature.
So we see once again that critics of the Catholic Church who claim she teaches a works-based gospel are flatly mistaken. We cannot earn by our works what by its very nature is beyond the reach of any merits we could ever have. God saves us. We cannot save ourselves.