When the heresiarch Arius tried to work out a logical doctrine of the Trinity to protect God's impassibility from the Passion of the Son, he made the error of dividing what should not be divided; namely, the "one substance" of the divinity, the unity of the three Persons. It is logical, if only by the standard of natural reason, but it fails in soteriology, and so ultimately failed to account for what it tried to account for.
It seems to me that there is a modern parallel in some circles of sacramental theology. Those who propose to do away with the "transitional" diaconate, as it is called, make the same error Arius once made, dividing the unity of the one sacramental reality of orders, so that the (purely natural) logic of the distinction between deacon and sacerdos will be clear.
In a similar way, this error also fails in soteriology. First, the proclamation of the Gospel - the invitation - must precede communion in the Holy Eucharist - the "banquet." If the priest does not receive the
sacra potestas of
kerugein as a deacon, the invitation is disconnected from the banquet, and our Holy Mass becomes two separate ritual actions, rather than one action with two parts. The salvific graces of hearing the Gospel then do not lead to and culminate in the Eucharist; while the Eucharist risks becoming ahistorical and mythologized, detached from the concrete Gospel proclamation.
Second, Christ was both deacon ("the servant of all") and priest (simultaneously victim, priest, and altar of the one perfect sacrifice); and indeed, He is both
in the same act of His Passion. If we detach these two aspects of His saving act in the sacrament of Order, we detach the two meanings of the act. Service and sacrifice then point away from each other, rather than to each other; and even, they become mutually exclusive meanings of the Passion. Service then leads only back into the world -- the "shipwreck of the world," recall -- and fails to connect in any meaningful way with grace. Sacrifice, meanwhile, again risks an ahistorical mythologizing, in which grace fails to penetrate to the level of everyday life (service).
Third, given that Christ did not institute the diaconate prior to His Passion, if the diaconate is detached from a meaningful relationship to the sacrifice of the ministerial priesthood, and hence from the actual graces of the Eucharist, how does one defend its sacramentality? In the same way, what becomes of the "fullness of orders" of the episcopate, and therefore of the whole doctrine of apostolic succession?
Arius's solution didn't work with respect to the Trinity. It doesn't work with respect to Holy Orders, either.
