We move from the Old to the New Testaments to understand what the Bible says about God. We reflect on how operations and missions tell us about God’s processional or inner life. And we find parallels in God’s created order by looking at our inner man.

Augustine wrote “On the Trinity” partly to guide readers in their knowledge of God. In this pursuit, he self-consciously followed dominical sayings such as, “And this is eternal life, that they know you, the only true God, and Jesus Christ whom you have sent” (John 17:3).

One key term that defines this journey is purify. Augustine believes that we need to purify our minds “because the weak eye of the human mind cannot be fixed on a light so dazzling, unless it has been nourished and become stronger by the justice of faith” (Aug., De Trin. 1.2.4).

To purify the mind, Augustine has something quite concrete in mind that follows the order of teaching contained within Scripture itself. As he says, “we must first find out by an appeal to the authority of the Sacred Scriptures whether faith is in a position to do so [i.e., reveal God to us]” (De Trin. 1.2.4).

Ultimately, his answer will be a qualified yes, provided “By [the principles of faith] a carefully-regulated piety,” heals our minds so we can “perceive the unchangeable truth” (De Trin. 1.2.4). In other words, Augustine’s ascent to God means that our whole self comes to know God.

How does he suggest we go about our pursuit of true knowledge of God?

First, it all begins with the faith once for all handed down to the saints. And that faith centers on inseparable operations, namely, that the Father, Son, and Spirit work inseparably in all that they do. Augustine emphasizes the unity of divine action—what later theology would call the principle that opera trinitatis ad extra sunt indivisa (the external works of the Trinity are undivided).

But the key point is: The one Lord Jesus Christ, the one God and Father of all, and the one Spirit of God inseparably operate in all they do, which evinces their unity of power, of substance, and ultimately their equality.

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