Summary of Chapter 20: Knowledge of the Triune God, from White’s book, The Trinity

We have concluded our study of the oneness of God by considering God’s inner life as a mystery of knowledge and love, one that invites us to think about the inner life of the Trinity. After all, it is the Father who, in knowing himself, eternally generates his begotten Word, and who, in loving himself, spirates the person of the Holy Spirit, who is love. It is fitting, then, in light of our consideration of God’s inner life, that we begin to pivot toward a consideration of the mystery of the Holy Trinity proper. This mystery will be the subject of the next section of this book. Here, however, as an epilogue to part 2 and as a kind of prolegomenon to part 3, we will consider the knowledge we have of the Holy Trinity and how we come by it.

Let us recall here some basic Thomistic epistemological claims. First, human beings can attain genuine natural knowledge of the existence and attributes of the one God by way of quia demonstrations from effect to cause, that argue from creaturely effects to the necessary existence of their transcendent Creator.

Q. Does the philosophical understanding of God by natural reason, which we can attain in this life, also permit us to obtain genuine natural or philosophical knowledge of God as Trinity?

Second, how does the claim that God is Trinity relate epistemologically. Aquinas on Rational Knowledge of the Trinity:

  1. When we seek to know God by natural reason, we seek to understand him from his effects of nature, that is, his creation. In so doing we can arrive at a certain knowledge of God understood as the causal principle of all created things.
  2. The creation bears indirect but real testimony to the existence of God and his divine attributes of simplicity, perfection, goodness, unity, power, and the rest, which pertain to God’s essence.
  3. The creative power of God, however, is common to the three persons of the Trinity; hence what we know of God from this power pertains to the unity of the divine essence, and not to the distinction of the persons.

Trinitarian belief is utterly monotheistic precisely because it claims that God is simple and one in essence (362). 

Substantive differences between Christians and Jews, and Christians and Muslims, with regard to the mystery of God are based primarily on different understandings of divine revelation, not on the truths that we can know about God by natural reason.