The Leitsatz (thesis statement) for §8 states: "God’s Word is God Himself in His revelation. For God reveals Himself as the Lord and according to Scripture this signifies for the concept of revelation that God Himself in unimpaired unity yet also in unimpaired distinction is Revealer, Revelation, and Revealedness."
In subsection §8.3 ("Vestigium Trinitatis"), Barth begins a discussion of the so-called vestiges of the Trinity:
But there is a danger in these "illustrations" - the illustrations can themselves become interpretations - and become the object of focus, rather than God. Barth thinks it is best to not even rely on the creaturely analogues that are illustrations of the trinity - and instead focus on the true vestigium which have been already created by God: the threefold form of Word, scripture, and proclamation:
The problem of the vestigial trinitatis [trace of the Trinity] which is posed by the history of the doctrine of the Trinity gives us cause to do this. This expression seems to come from Augustine and it means an analogue of the Trinity, of the trinitarian God of Christian revelation, in some creaturely reality distinct from Him, a creaturely reality which is not a form assumed by God in His revelation, but which quite apart from God’s revelation manifests in its own structure by creation a certain similarity to the structure of the trinitarian concept of God, so that it may be regarded as an image of the trinitarian God Himself (334).Barth wants to consider the fact that many theologians have looked for and supposedly found analogues of the trinity in "creaturely" things - a point which concerns him because it has the potential of becoming a "second root" of the doctrine of the Trinity - one that would exist independently of revelation:
The concern here was with an essential trinitarian disposition supposedly immanent in some created realities quite apart from their possible conscription by God’s revelation. It was with a genuine analogia entis [analogy of being], with traces of the trinitarian Creator God in being as such, in its pure createdness. If it be acknowledged that there are vestige trinitatis [traces of the Trinity] in this second sense then the question obviously arises—and this is why we must discuss the matter in the present context—whether we do not have to assume a second root of the doctrine of the Trinity along-side the one we have indicated in the previous sub-section. The vestigial trinitatis [trace of the Trinity] would patently have to be considered as a second root of this kind if there is such a thing in the second sense of the term. We should then have to ask whether the development of the doctrine of the Trinity must not also, at least, be traced back to the insight into these traces of the Trinity that are present and perceptible in the created world quite apart from the biblical revelation" (334-335).What Barth is noting is that there is a danger in in attempting to produce conceptual analogies of the trinity from human experience because, as Alan Torrance points out in his excellent article on the Trinity in The Cambridge Companion to Karl Barth, "the pressure of interpretation is found to be directed from these analogues to revelation (such that they themselves risk becoming the root of the doctrine) rather than the other way around as revelation demands. To endorse thinking about God from some control on our thinking, other than the unique content of context of revelation itself, is to risk admitting into the theological illiim a Trojan Horse..." (80). Here is Barth,
The question is whether these vestigia trinitatis, in virtue of the conclusions that are to be drawn from their acknowledgment even if only in the form of the list of questions mentioned, do not compel us to pass over first to the easy double track of “revelation” and “primal revelation” (P. Althaus) and then very quickly from this half-measure to the genuine Roman Catholic theology of the analogia entis. And then would they not bring to our attention at the right moment the fact that theology would do well to desist from the impossible attempt to understand itself as theology and to acquiesce in being the only thing it can be at root, namely, part of man’s understanding of the world and himself, in the development of which the concept “God,” like a superfluous x in the numerator and denominator, should now be cancelled out to simplify the counting on both sides, since with or without the concept the only real concern is man, or, in this case, man’s own triunity. But the question can, of course, be put in a very different way: Do we not have in this idea of the vestigium trinitatis an ancient Trojan horse which one day (for the sake of pulchritude [beauty] and delectation [delight], to echo Augustine) was unsuspectingly allowed entry into the theological Ilium, and in whose belly—so much more alert have certain experiences made us since Augustine’s day—we can hear a threatening clank, so that we have every cause to execute a defensive movement—perhaps there is no more we can do here—by declaring, perhaps only very naively, that we do not want to have anything to do with it? (335-336).Barth categorizes these vestigia trinitatis into five groupings: nature (336), culture (336), history (337), religion (337), and the human soul (or psychology, 337-338). He contends that there's really no problem with these analogues, just so long as we realize they are just "interesting, edifying, instructive and helpful hints towards understanding the Christian doctrine, not to be overrated, not to be used as a proof in the strict sense, because we need to know and believe the Trinity already if we are really to perceive its vestigia as such in the microcosm and the macrocosm, but still to be valued as supplementary and non-obligatory illustrations of the Christian Credo which are to be received with gratitude" (338). In other words, these are helpful, just so long as these are seen in the light of revelation - not as a "second root."
But there is a danger in these "illustrations" - the illustrations can themselves become interpretations - and become the object of focus, rather than God. Barth thinks it is best to not even rely on the creaturely analogues that are illustrations of the trinity - and instead focus on the true vestigium which have been already created by God: the threefold form of Word, scripture, and proclamation:
There is of course, and with this we close, a true vestigium trinitatis in creature [trace of the trinity in the creature], an illustration of revelation, but we have neither to discover it nor to bring it into force ourselves, As we have tried to understand it as the true and legitimate point of the vestigia doctrine, it consists in the form which God Himself in His revelation has assumed in our language, world, and humanity. What we hear when with our human ears and concepts we listen to God’s revelation, what we perceive (and can perceive as men) in Scripture, what proclamation of the Word of God actually is in our lives—is the thrice single voice of the Father, the Son, and the Spirit. This is how God is present for us in His revelation. This is how He Himself obviously creates a vestigium of Himself and His triunity. We are not adding anything but simply saying the same thing when we point out that God is present for us in the threefold form of His Word, in His revelation, in Holy Scripture, and in proclamation.
This vestigium is plain and reliable. It is the vestigium of the God who deserves to be called God. It is really the vestigium of the triune God in the sense of the Church doctrine of the Trinity. But this vestigium is better described as vestigium creaturae in trinitate [trace of the trinity in the creature] as noted earlier. In adhering to this, we shall not be accepting a second root alongside the first but just the one root of the doctrine of the Trinity (347).Indeed!