I spent some spare time over a few months reading portions of the Summa Theologica related to justification. I'm planning on doing a series of posts on the results.
I do not pretend that I will be offering anything like comprehensive coverage of St. Thomas' treatment of the subject. In the first place I'm not a theologian or philosopher. I'm just this guy, you know? So anyone expecting an academic treatment will be disappointed. In the second place, I'm not an Aquinas scholar; I'm merely an earnest enthusiast for his work. My reading has been almost entirely driven by a "dictionary search" - that is, a search of the Summa for passages that mention "justification". This is, admittedly, terribly simplistic; but I suspect it's safe to say that whatever nuances might be missed this way, in the main I'll be covering the major themes.
A major defect of these posts is that they are without question going to seem somewhat disconnected if they are taken all together as a collection. I am not posting sections or segments from a larger, complete paper on the subject, which one could rightly expect to have some manner of unity; rather, my expectation is that each post will stand alone for the most part. I'm not an academic, and I don't have time to synthesize this material properly for a complete standalone paper. But I'm also taking the venue and audience into consideration. In my opinion a blog is a poor place for lengthy articles. People don't read blogs like they read books; they read them more like they read magazine articles or (ugh) watch TV. So it seems better to keep blog posts relatively short, and use tags to allow folks the opportunity to do further reading on a subject when they want.
Why am I doing this series? Because it's my blog, and I get to do what I want with it :-) But I'm also doing it as something of an apologetic exercise. Many (most?) Protestants have a grossly distorted idea about what the Catholic doctrine of justification looks like. I hope to set the record straight to some extent, and St. Thomas is an excellent representative for what the Church has always taught about the subject. He was, like his fellow medievals and schoolmen, strongly conservative with respect to theology. Aquinas' genius was not in the way of novelty. He is also one of the Doctors of the Church, "on account of the great advantage the whole Church has derived" from his work (cf. previous link).
I hope these posts will be interesting and useful to you.