Herman Bavinck, Reformed Dogmatics, abridged, p. 230:
For the Christian church. the doctrine of the Trinity was the dogma and hence the mystery par excellence. The essence of Christianity–the absolute self-revleation of God in the person of Christ and the absolute self-communication of God in the Holy Spirit–could only be maintained, the church believed, if it was grounded int he ontological Trinity. To defend Scripture’s teaching, the church found it necessary to use language that went beyond Scripture, a practice condemned by Arians and their post-Reformation and modern counterparts but always defended by Christian theology. Christian theological reflection on Scripture has every right to move freely beyond the exact language of Scripture to draw warranted inferences from it. These two are authoritative. In fact, theological reflection on Scripture is not even possible without the freedom to use extrabiblical terminology. Their use is not designed to introduce new–extrabiblical or antibiblical–dogmas but, on the contrary, to defend the truth of Scripture against all heresy. They exercise a primarily negative function, marking the boundary lines within which Christian thought must proceed in order to preserve the truth of revelation.
Steven Boyer and Christopher Hall, The Mystery of God, p. 121:
God is not just tri-personal; he is expansively, creatively tri-personal. The triunity of God is something taht unfolds and opens out, not something that curves in and closes down on itself. God’s intrinsic relational completeness, the unimaginable eternal intimacy between the Father and the Son in the Spirit, does not exclude other relations; it is instead the ground of other relations. The unquenchable divine joy that makes creation unnecessary also makes creation possible in the first place, for the love of Father, Son, and Spirit is in no way threatened or imperiled by flowing out beyond itself into a created world. […] God is love, and creation itself is a wholly free outpouring of that love, in generous, gratuitous, open-handed bounty, a bounty that is infinitely hospitable not because it needs us but simply because it is itself.
Millard Erickson, Christian Theology, 2nd ed., pp. 366-67:
Although we cannot fully see how these two contrasting conceptions [oneness of God; threeness of God] relate to each other, theologians are not the only ones who must retain two polarities as they function. In order to account for the phenomena of light, physicists have to hold both that it is waves and taht it is quanta, little bundles of energy as it were, yet logically it cannot be both. As one physicist put it: “On Monday, Wednesday, and Friday, we think of light as waves; on Tuesday, Thursday, and Saturday, we think of it as particles of energy.” Presumably, on Sundays physicists do not concern themselves with the nature of light. One cannot explain a mystery, but can only acknowledge its presence.
Khaled Anatolios, Retrieving Nicaea, pp. 6-7:
The use of analogies has been pervasive in the history of Christian reflection on the divine Trinity. But, going beyond skirmishes over which analogy is most adequate, one has to question the whole approach in which analogies become the primary location of trinitarian meaning. When the meaning of trinitarian doctrine is located principally in some particular creaturely analogue, it becomes separable from other aspects of the Christian mystery. Instead of trinitarian meaning being embedded in the whole nexus of Christian faith, it tends to be reduced to the features of the analogue itself. One can after all espouse “relationality” or wonder at the mind’s differentiated unity in the acts of knowing and willing without actually confessing and worshiping the Triune god as Father, Son, and Spirit. In that case, one could capture the meaning of trinitarian doctrine without ever subscribing to Christian faith. At the very least, the doctrine of the Trinity is then in danger of becoming simply another item in the list of Christian beliefs. Thus a Christian would be someone who believes that God created the world from nothing, that Jesus arose from the dead, and that God is in some way like a shamrock leaf (or human consciousness, or human relationships). Surely Rahner is right: the meaning of trinitarian doctrine must have a more intrinsic connection to the structure and texture of the whole of Christian life and faith.