Two chapters from Alister McGrath’s Christian Theology: An Introduction focuses on the doctrines of God and of the Trinity.
The first concern addressed is the doctrine of God. McGrath offers the minor theory that God might not be male and quickly moves forward. He identifies the “personhood” of God through such philosophers as Tertullian, Spinoza, and Buber. These offered what God’s love towards man looked like while retaining His omnipotence, omniscience, and omnipresence (199-203). McGrath discusses the emotions of God, namely the possibility for God to suffer. Aquinas and Moltmann provides McGrath’s two examples. Aquinas: “Mercy is especially to be attributed to God, provided that it is considered as an effect, not as a feeling of suffering” (204). Conversely, from Moltmann, “a God who cannot suffer is a deficient, not a perfect, God” and “God willed to undergo suffering. The suffering of God is the direct consequence of the divine decision to suffer and the divine willingness to suffer” (206). McGrath briefly offers Patripassianism, God suffering with Jesus, and Theopaschitism, “one of the Trinity was crucified” (207); the latter, superficially, implies modalism. Next, McGrath discusses God’s power through omnipotence, need for self-limitation, and influence and persuasion (209-215). In this section, McGrath implies the age-old question of “Why bad things happen to good people?” using the theory of process theology (214-215). McGrath addresses the “goodness” or, conversely, the benign nature of God’s creation and shares theories from Tertullian, Irenaeus, Augustine of Hippo, Barth, and Plantinga (215-227). He admits that the Holy Spirit deserves a dedicated chapter and yet briefly offers aspects and functions of the Spirit within the life of man (227-233).
Next, McGrath discusses the Trinity and how each part of the Trinity fulfills his nature. Homoousios and homoiousios are both features of God and Jesus that McGrath identifies (235-236). McGrath notes, “the proper subject matter of the doctrine of the Trinity is the encounter between divine and human persons in the economy of salvation” (236). The “hypostasizations…point to a pattern of divine activity and presence in and through creation, in which God is both immanent and transcendent” (239). McGrath notes the difference between persona of the Trinity from the substantia (240) and discusses two heresies of the Trinity: modalism and tritheism (244-246). The Cappadocian fathers discussed the filioque controversy as understanding the relationship and movements of the Spirit and Jesus to God (247-249). McGrath concludes this chapter by offering perspectives on the Trinity from: Augustine, Barth, Rahner, Macquarrie, Jenson. Of note from Rahner, “the way God is revealed and experienced in history corresponds to the way in which God actually is” (254). In other words, God will not reveal Himself contrary to His nature, and man may discover His nature through history.
Ultimately, Karl Barth best addresses the power, ability, and function of God and the Trinity: “For revelation to be revelation, God must be capable of effecting self-revelation to sinful humanity, despite their sinfulness” (253).