Attention to the doctrine of inseparable operations (DIO) of the Trinity protects us from being either functional unitarians, or functional tritheists. Functional unitarians disregard the real distinctions between the divine persons; functional tritheists divide the divine nature. True Biblical trinitarianism is not affirmed solely by attention to DIO, but the latter forces us to properly interpret the ‘economic’ actions of the divine persons. What does this look like in practice?

  1. Creation. While Irenaeus’ metaphor of the Son and Spirit as the hands of God is helpful, we must resist thinking of them as ‘instrumental agents’ of the Father’s work. Neither, however, is the Son simply the (Platonic) ‘mind’ of an undifferentiated God. The differentiation of the persons must be preserved as much as the unity of substance. But how?
  2. Incarnation. The Son comes, but not such that the Father is only extrinsically ‘represented’ by the Son. The mutual indwelling of the Father, and Son, and Spirit is precisely what makes the incarnation salvific. Christ is not yet another intermediary, but the fullness of the divine Trinity. Yet only the Son has become incarnate, not the Father, or the Spirit.
  3. Actions of the Incarnate Son. How does the inseparable agency of the trinitarian persons deploy through the hypostatic union? This is a perplexing question. On the one hand we want to affirm that God is acting in Christ; on the other hand, we want to retain Christ’s representativeness for us (that we may identify with him and follow him). The dilemma is as follows: on the one hand, unless Jesus is God acting for the reconciliation of the world, he may not be regarded as our Savior. On the other hand, unless Jesus is a real human being with whose actions we may identify (resisting temptation, miracles?), he is of no priestly use to us.
  4. Cross. Does the Father abandon the Son at the cross? DIO suggests that any such abandonment is unthinkable, when the Son is regarded in terms of his divine nature. The Father-Son relation is constitutive of their eternal identities. Break that relation and you are braking the person, and hence God. DIO must be nimble enough to provide for the ‘dereliction’ of the Son, but also for the substantial unity with the Father, whilst also avoiding Patripassianism (the heresy that the Father suffers and dies on the cross).
  5. Ascension and Pentecost. This is an especially interesting instance of inseparable operations. The gospels seem to indicate something like a player substitution: the Son must depart in order for the Spirit to arrive. It is almost as if the Son and Spirit cannot both occupy the same space. This must be a false impression. Jesus promises to be with us forever. Somehow that presence takes place through the Spirit, however. How do we understand this ‘substitution’?
  6. Indwelling of the Spirit. Related to the previous question, we are temples of the Holy Spirit. Christ has ascended, yet he is also indwelling us (Rom 8:10, etc.). Why, then, does the NT speak primarily about the indwelling of the Spirit? In what way are we to understand that there is a unique indwelling of the Spirit, which is not simply the same thing as the presence of Christ, yet inseparable from it? The implications of working through this question bear on the relationship between justification and sanctification, but also on the question of the agency of the Spirit in the church. What is the significance of the bodily absence of Christ? May the Church, or believers, be regarded as continuations of the incarnation? Does the Spirit self-communicate himself to us in a way analogous to the self-communication of the Son to the human nature of Jesus? Finally, how is the indwelling of the Spirit now related to the ultimate seeing of God, the beatific vision?