Dabney distinguished between expiation, which is Christ's work on behalf of sinners, and atonement, which is actual reconciliation -- "at-one-ment". Here is a quote from Dabney's Systematic Theology apropos to the subject:
It seems plain that the vagueness and ambiguity of the modern term 'atonement,' has very much complicated the debate. This word, not classical in the Reformed theology, is used sometimes for satisfaction for guilt, sometimes for the reconciliation ensuing thereon; until men on both sides of the debate have forgotten the distinction. The one is cause; the other effect. The only New Testament sense the word atonement has is that of katallage, reconciliation. But expiation is another idea. Katallage is personal. Exilasmos is impersonal. katallage is multiplied, being repeated as often as a sinner comes to the expiatory blood: exilasmos is single, unique, complete; and, in itself considered, has no more relation to one man's sins than another. As it is applied in effectual calling, it becomes personal, and receives a limitation. But in itself, limitation is irrelevant to it. Hence, when men use the word atonement, as they so often do, in the sense of expiation, the phrases, 'limited atonement,' 'particular atonement,' have no meaning. Redemption is limited, i.e., to true believers, and is particular. Expiation is not limited."
Page 528. Sorry about the transliteration of the Greek. I don't care to figure out how to do Greek fonts for the blog.
Many modern day Calvinists of the Presbyterian and Reformed Baptist variety would balk at this, but Dabney clearly doesn't wish to limit the expiatory work of Christ. The reconciliation that is the effect of the expiation clearly is limited to believers; but Christ's work itself is not limited. Here is where the old formula, "sufficient for all, efficient for the elect" seems just right. The expiation is sufficient for all, intended for all, and offered to all. Whereas the reconciliation effected by that expiation is efficient only for believers and intended only for believers. How this interacts with the doctrine of election is the subject for the next blog.
To close, here is Calvin's comment, in part, on 1John 2:2, where he approves the formula "sufficient for all, efficient for the elect":
"Here a question may be raised, how have the sins of the whole world been expiated? I pass by the dotages of the fanatics, who under this pretense extend salvation to all the reprobate, and therefore to Satan himself. Such a monstrous thing deserves no refutation. They who seek to avoid this absurdity, have said that Christ suffered sufficiently for the whole world, but efficiently only for the elect. This solution has commonly prevailed in the schools. Though then I allow that what has been said is true, yet I deny that it is suitable to this passage...."