St Thomas appears to say that it can, at least when the cause is the humanity of Christ, acting as a ‘conjoined instrument’ of the Word. In question 48 of the Tertia Pars, describing the various different ways in which our Lord’s passion saves us, he comes in article 6 to the question of efficient causality. Does Christ’s passion act an efficient cause? That is, does it cause grace in the soul by literally acting on the soul, as literally as, say, a sculptor shapes a block of marble by acting on it with hammer and chisel? St Thomas says that it does. To the objection that Christ’s passion was limited to one time and place, and so can’t literally ‘touch’ people of all times and places, he says that it can, because of the ‘spiritual power coming from the divinity united’ to His suffering body and soul. This spiritual power of the suffering Christ touches our soul by faith and the sacraments of faith as really as the chisel touches the marble.

Yet how can it? When Abraham, for example, was justified, the passion of our Lord was still 2,000 years in the future. That which doesn’t exist cannot act. I think St Thomas would reply that the Word existed when Abraham was justified; and the existence of the Word is simultaneous with all times; and so the Word, having the passion of Christ simultaneous to it, could exercise its power through the passion of Christ on another object that was simultaneous to it, namely Abraham’s justification, even though these two earthly events, the Passion and Abraham, were not simultaneous to each other.

(Technical note: one might object: simultaneity is a transitive relation: if A is simultaneous with B and with C, then B and C must be simultaneous. The answer to this is that simultaneity is only transitive whilst one remains in the same ‘kind’ of duration, for example within time, or within the angelic ‘aevum’, or within eternity. But when one considers simultaneity across different ‘kinds’ of duration, it is no longer transitive).

This at least is Abbot Vonier’s reading of St Thomas. Cajetan, if I remember correctly, plays down St Thomas’s words, and seems to think that nothing can literally act upon things which are not simultaneously present to it, and so that the actual suffering, or resurrection, or ascension of Christ are not strictly efficient causes. But I think Vonier is faithful to St Thomas here; and, even more importantly, to the language of St Paul.