For Mark, because the Master Jesus ordered Christians to pray for the Spirit, and because he ordered the apostles to "do this in memory of me," only confidence in the Master versus automatic causality of a human efficient cause changes the gifts through the Spirit. (p. 132)
Reading the whole book one can kinda-sorta get an idea of what Kappes must really be intending, but the sentence as it stands is gibberish. None of the accounts on the table -- Thomistic, Bonaventuran, Scotist, or Byzantine -- takes anything about the sacrament to be "automatic"; and one of the things they all agree on is that it is a divine gift. In the context of Thomistic instrumental causality, one might as well as say that poems are automatically created by pens when poets set them to paper; it's not just wrong, it makes no sense. But more seriously, Mark, of course, never commits to such an obvious absurdity as "confidence in the Master...changes the gifts through the Spirit". At no point will you find Mark saying that our confidence turns the bread and wine to body and blood, or anything like it; it is inconsistent with his account. And Mark's concern in the argument being described here is not confidence vs. automatic causality but something else entirely.
The essential issue, of course, is that the Latin view of the Eucharist is that the bread and wine become Body and Blood at the words of institution, the words Christ used at the Last Supper to institute the sacrament -- 'This is my body' and 'This is my blood', although some Latins took it to be a larger amount of the prayer in which these words are embedded. The Greek view is that they become Body and Blood after the words of institution at the epiclesis, which is the prayer for the Holy Spirit to come down upon the offering. The divergence is quite natural, because it arises from the simplest reading of the prayers of the divine liturgy in each case. The Roman Canon at the time of the Council of Florence had no formal epiclesis, although some (the great Nicholas Cabasilas, for instance) had argued that one of its prayers, the Supplices te rogamus worked functionally as an epiclesis. But even if one takes Cabasilas to be right, after the words of institution, the most natural reading of all the prayers is that the Body and the Blood are already present. In the major Eastern liturgies, the epicleses are framed in terms that naturally suggest that the priest is praying in the epiclesis for the bread and wine to become the Body and the Blood, meaning that they still have not become the Eucharist in the proper sense. The difference leads to further differences; the natural implication of the Latin view is that only the words of the institution are required to have the Eucharist. The Greek view, on the other hand, does not naturally suggest the same about the epiclesis; the epiclesis is referring to things that have already been going on in the prayer of the divine liturgy, so it is natural to read it as the culmination, the final thing put into place to get the sacrament.
One of the really interesting things in the book is the view put forward by Mark of Ephesus on behalf of the Greeks at Florence. Kappes jumps around more than he should in explaining this absolutely central contribution, but it becomes clear what Mark's view is when you read Mark's Libellus, which Kappes provides in Appendix II. Both Mark and his opponent, Torquemada, agree that Christ's words are essential to the sacrament. But here is the fundamental difference: on Mark's view, the priest's statement of them is nothing but a commemoration. Christ's words, the very words on Holy Thursday, are essential to the sacrament. Christ's words have causal power to effect the sacrament, and without them there would be no sacrament. But we don't participate in the sacrament until the Holy Spirit is called down upon the altar and makes the elements the Body and the Blood. In preparation for this prayer, the priest remembers Christ's words. But the only thing the priest's commemoration of those words contributes is precisely that: commemoration. It is Christ's words that carry the power that makes the sacrament possible; in the epiclesis the priest prays for the Holy Spirit to actualize this power, and the Holy Spirit does.
One thing I find interesting is that this means that Mark's view has affinities with the Thomistic or instrumentalist view. Kappes repeatedly contrasts the Ephesine view with the Thomistic view, which is not surprising, since the major Latin opponent of it, Torquemada, accepted the Thomistic view. He also tends to associate the Ephesine view with a different view, the Scotist or occasionalist view. This is fashionable, but as Mark presents the view in the Libellus, the Ephesine view is actually intermediate between the instrumentalist and the occasionalist views.
On the occasionalist view at its simplest, there is a pact or promise between God and the Church; when the priest prays, God does what was promised. The priest's prayer is only an occasion for God's separate action of giving grace.
On the instrumentalist view found in Aquinas, however, God works through and in lesser causes, so that grace is given through and in these lesser causes, like a blacksmith uses a hammer to make something (to use Torquemada's analogy) or like a poet uses a pen to write poems (to use the Bañezian analogy that eventually became popular). The result of the blacksmith's use of the hammer goes beyond anything the hammer could do on its own, because it is the effect of the blacksmith, but it's not as if the hammer just does its own inadequate thing and then the blacksmith intervenes and makes the result; the blacksmith makes the result through the hammer. The most fundamental instance of this in the case of the grace is, on the Thomistic view, Christ's human nature, which is an instrument that is conjoined to the agent who uses it (like the hand of the blacksmith). The sacraments are extensions of this; they are separate instruments that are able to be instruments at all only because of their relation to the conjoined instrument (like the hammer in the hand of the blacksmith). All sacraments are actions of Christ, but in consecrating the Eucharist the priest serves as an instrument of Christ, so that when the priest says the words of institution, this is an act not merely of the priest (the hammer) but of Christ (the blacksmith). The priest says Christ's words like a pen writes a poet's words.
On the Ephesine view, as noted above, Christ's words on Holy Thursday have consecrating power; they are like God's commands at creation. Without them there would be no Eucharist; they make it possible. But this needs completion in the specific sense that there needs to be something that makes the sacrament here and now for us. The priest cooperates with the divine power of Christ's words by obeying the command to remember them and by performing the relevant blessings. But the change is effected by the Holy Spirit's descent on the altar when the priest prays for Him to do so. This view is much more robust than a strict occasionalist view; to say that Christ's human words have causal power in the sacrament is not occasionalism. It is indeed something an instrumentalist would say, not an occasionalist. The Ephesine view does not, however, give an instrumentalist account of the sacrament itself. The priest's words are not Christ's words; they're just a memorial of them.
From the evidence Kappes gathers in his book, it is very clear that the Latins were very confused by this, and whenever the Greeks talked about Christ's words, they seem generally to have taken it to mean Christ's words as said by the priest at Mass, not Christ's words centuries ago on Holy Thursday, to which Mark actually attributes real power. This seems to be why, for instance, they were utterly baffled at the Byzantine analogies to creation and the Annunciation; they kept thinking that the Byzantines meant that when the priest says 'This is my body' that we then have the Body but defectively until the epiclesis, whereas Mark, at least, meant that Christ's words on Holy Thursday, of which the priest reminds us, are what makes the Eucharist possible and the Holy Spirit descending at the epiclesis makes it actual.
For an instrumentalist, Christ has real power that is exercised in the sacrament but the priest is an instrument of this real power, so Christ's words said by the priest are instrumentally Christ's, through which He performs the sacrifice. This is not true in Mark's account; the words of institution are just a memorial, and the Holy Spirit's descent on the altar, while it is because of the priest's prayer, is not through the priest as instrument. It is this that makes Kappes and others tend to overassimilate Mark to the occasionalist view. In a sense we could say that Mark is instrumentalist about Christ's participation in the Eucharist and occasionalist about the priest's. If you only focus on the priest, he will look occasionalist; but it is impossible for an instrumentalist to focus only on the priest -- instruments, as instruments, only work as they do because of their principal agents. Both the Ephesine and the Thomistic view attribute real causal work in the sacrament to the same principal agent, Christ; but the Thomistic view takes this real causal work in the sacrament itself to be through the priest, who is a 'moved mover', so that the priest's actions are part of Christ's action, whereas the Ephesine view takes this real causal work to be something with which the priest cooperates non-instrumentally, by obeying the commands to commemorate and to pray for the Holy Spirit, while Christ and the Holy Spirit achieve the result by actions distinct from anything the priest himself does.
Christiaan Kappes, The Epiclesis Debate at the Council of Florence, University of Notre Dame Press (Notre Dame, IN: 2019).
For a convenient introduction to the basics of Thomistic instrumentalism (of which you will not get any clear picture in Kappes's book), see Reginald M. Lynch, O.P., The Cleansing of the Heart: The Sacraments as Instrumental Causes in the Thomistic Tradition, The Catholic University of America Press (Washington, DC: 2017).