Question: How has the concept of the Trinity in Christianity affected relations with other monotheistic faiths?
In considering and reflecting on this question, it seems prudent to identify the two other major monotheistic faiths as Islam and Judaism – both of which consider Christian Trinitarian doctrine heretical, and therefore a severe stumbling block to relations at this level.
Islam apparently focuses on Deuteronomy 6:4 (McGrath, 247), where the Hebrew God clearly indicates that the Lord is one. The assumption is, therefore, that by proposing that Jesus and the Spirit are both God also, Christians accept a tritheistic stance. However, this assumption is obviously flawed and counter to accepted theology: Tertullian, in particular, hammered out the axiom that the Trinitus is made up of three personae with unius substantae.
For Judaism, the Christian Trinity has an immediate heresy: that of recognizing Christ as the Son, and therefore the Messiah. Interestingly though, the Law and the Prophets – that is, the Old Testament Scriptures – lay down firm foundations for Trinitarian Doctrine (McGrath, 248; De Colle, 122) through three personifications of the God of the Hebrews: the personification of Wisdom (especially in Job, Proverbs etc.), active in creation; the Word of God, going forth into the world to confront man throughout the OT; and the Spirit of God, His presence and power within creation. If only Judaism paid heed to the Johannic Logos – where that very same “Word became flesh and dwelt amongst us” (John 1:14) they might recognise Jesus for what He was – begotten of the Father, who with that same Father and the Spirit make up our triune, paradoxical Godhead.
R De Colle, ‘The Triune God’ in C Gunton, (ed.), The Cambridge Companion to Christian Doctrine, (Cambridge: CUP, 1998), pp. 243-71.
A McGrath, Christian Thelogy: An Introduction, fourth ed. (Oxford: Blackwell 2007) pp. 243-71.