Nevertheless the Fathers of old were justified by faith in Christ's Passion, just as we are. And the sacraments of the old Law were a kind of protestation of that faith, inasmuch as they signified Christ's Passion and its effects. It is therefore manifest that the sacraments of the Old Law were not endowed with any power by which they conduced to the bestowal of justifying grace: and they merely signified faith by which men were justified.
For our purposes in this series, two things are of interest here. First, St. Thomas affirms that we are justified by faith (as we saw in a previous post). Of course, this is not to say that our works are of no value, as we saw; but it does mean that the Protestant who claims we believe a "works-based" gospel is badly misinformed.
Secondly, it's clear that the only way that the Old Testament Fathers could have had the faith that St. Thomas describes here is implicitly: for they knew neither his name, nor the day of his coming. And this is consistent with what we have seen previously about implicit faith.