I'm almost finished with a small (five page) essay summarizing some of the main points of St. Thomas's trinitarian theology and putting them in relation to John 5:17-20. I had never realized before how much St. Thomas likes appropriate numerations. For example, the first part of the Summa begins with a treatise on the unity of God. The treatise on the Trinity then begins at question no. 27 (3x3x3). The next treatise, on creation, begins at question no. 44 (4 winds, 4 corners of the earth, etc.). Within the treatise on the Trinity there is one question on the Father (q. 33), two on the Son (qq. 34-35), and three on the Holy Spirit (qq. 36-38). Furthermore, his entire theology of God can be summarized thus:
The essence, of course, is the divine nature; the processions are of the intellect and of the will; the persons are Father, Son, and Holy Spirit; the relations are fatherhood, sonship, spiration (breathing forth), and procession; and the notions are the four relations plus innascibility (being ungenerated) as regards the Father.
Quite remarkable, I think.
[UPDATE] The paper is available via the link on the sidebar.