The classic formulation of the sufficiency/efficiency distinction in discussions of the atonement is found in the third book of Peter Lombard’s Sentences, in the third chapter of the twentieth distinctio. We will probably read this chapter as a whole in the Davenant Latin Institute’s “Advanced Early Modern Latin Reading” course. For the time being, here is the famous opening sentence.
All hangs on the fact that, though etymologically related, sufficientia and efficacia have different meanings: “sufficiency” has to do with making satisfaction, with “doing enough”; “efficiency” has to do with bringing about a desired result, producing, executing, accomplishing, completing something–in this case, it has to do with applying the sufficiency of the death of Christ to particular individuals and thereby saving them from eternal ruin.
Christus ergo est sacerdos, idemque et hostia pretium nostrae reconciliationis: qui se in ara crucis non diabolo, sed Trinitati obtulit pro omnibus, quantum ad pretii sufficientiam: sed pro electis tantum, quantum ad efficaciam, quia praedesitnatis tantum salutem effecit. (Sententiarum libri quatuor 3.20.3)
“Christ therefore is the priest, and the same one is also the sacrificial victim, the price of our reconciliation–1who on the altar of the cross offered himself not to the Devil, but to the Trinity, on behalf of all, in so far as it pertains to the sufficiency of the price, but for the elect alone, in so far as it pertains to efficacy, because he has effected salvation for the predestined alone.”2