The Bible, meaning the Old and New Testament put together, tells us of God’s dealing with mankind in three distinct ways or through three distinct persons (NT ref. see 2 Cor 13:13, Matthew 28:19). But it also emphatically holds that there is only one single God. The doctrine of the Trinity is thus a description of a one God, in substance, who exists in three persons. He is transcendent, the creator and sustainer, but incarnated Himself in the world as Jesus Christ, who for His part already existed before the beginning (John 1:1ff), and also guides us and lives in us as the Holy Spirit (McGrath 2011:236). However, Scripture does not actually contain a doctrine of Trinity but shows us “a God who demands to be understood in a trinitarian manner” (McGrath 2011:239). Therefore many theologians have felt the need to expound the subject.
The Cappadocian fathers were the first to establish the doctrine of the Trinity, in Constantinople 381 AD. This model is relevant today in the eastern churches (i.e. Greek and Russian Orthodox). The basic statement is that the Trinity is “one substance in three persons”: one God exist simultaneously in three modes of being. Tough they have/are the same substance, and are thus equal, the Father is the fountainhead from which the Son is begotten and the Spirit proceeds. (McGrath 2011:249f)
The Eleventh Council of Toledo which met in the year 675 AD formulated a traditionally western approach to the Trinity. According to the 11 bishops there present God is not to be spoken of as triplex but triune, nor can we say that the Trinity is in the one God but that the one God is the Trinity. The Trinity is God’s way of relating to Himself: Father and Son to each other and the Holy Spirit to both. The difference between them is not one of substance, but relation. Their inter-relation is what defines them. The Son is begotten by the Father, and the Spirit proceeds from them both. And all are equal. (McGrath 2011:246, 249)
Karl Rahner (1904-84) concentrated on giving “economic” Trinity, God’s appearance to us, and “immanent” Trinity, God as He is in heaven, equal importance and status to correct tendencies within (older) Catholic trinitarian theology to focus on immanent trinity so much that God’s salvation of humankind is overshadowed. How God shows Himself to us is the same as He is, there is no difference according to Rahner. The doctrine of the Trinity is thus not something that humans adopt to understand God‘s revealing Himself, but God behind the revelation is Trinitarian too. (McGrath 2011:254f)Sources: Althaus, Paul, The Theology of Martin Luther, Philadelphia: Fortress Press 1966 Henriksen, Jan-Olav: Guds virkelighet: Kristen dogmatikk (God’s Reality: Christian Dogmatics), Oslo: Luther Forlag 1994 McGrath, Alister E. Christian Theology. An Introduction. Oxford: Blackwell 2011 Svenska kyrkans bekännelseskrifter (Church of Sweden’s Book of Creeds), Stockholm: Verbum 1997
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