What is Hume Doing In His Essay “Of Miracles”?

Much of the scholarship having to do with Hume’s argument against miracles has to do with trying to understand it. Philosopher Michael Levine claims Part I of Hume’s essay is an "a priori" case against miracles (The Cambridge Companion to Miracles, p. 302) based on considerations of natural law before there's a miracle claim--that the evidence of natural law outweighs any testimony to a miracle--whereas Part II is an a posteriori case against miracles, “even if miracles have occurred.” (p. 293).
About Hume’s principal argument in Part I, Levine says “it fails” (p. 296) as an “unsuccessful” (p. 292) “superfluous” (p. 302) “misadventure” (p. 292). “It is a gloss for understanding the underlying supposition that one cannot have an ‘impression’ of a supernatural event” (p. 302). This underlying empiricist supposition is a theme of Hume’s, in which he argues we don’t have empirical sense impressions of ‘cause and effect’ or any divine activity, or the self for that matter, which is nothing but a bundle of sensations. So “Given his view that divine activity is impossible to know, Hume’s argument in Part I is in a sense superfluous” (p. 302).
Part I presupposes naturalism, Levine says. Philosophers like him, who rule out the possibility of miracles “are in effect presupposing or else arguing for a thoroughgoing naturalism. Hence, Hume’s empiricism commits him to naturalism, and if that goes unrecognized, his a priori argument in Part I of his essay against the possibility of justified belief in miracles is impossible to follow.” (p. 292). All one has to admit is that “naturalism is possibly false.” Once this is admitted “miracles are possible.” (p. 292).
Hume is thus constrained by his empiricism in such a way that had he been on the shore of the Red Sea with Moses, and had the Red Sea crashed to a close the moment the last Israelite was safe, Hume would still be constrained by his principles to deny that what was witnessing was a miracle (p. 298).

In Part II of Hume’s essay he tackles the a posteriori question of what to do “even if miracles have occurred.” Here Hume deals with the only significant philosophical question that matters: “Is anyone justified in believing in miracles—for example, on the basis of Scripture” (p. 296).  “This is the question that many philosophers on miracles either (1) ignore or postpone—while addressing questions about laws of nature instead; (2) affirm—despite what historical scholarship and sophisticated biblical (textual) criticism tell us; or (3) casually presuppose to be answered affirmatively” (p. 296). On this crucial question Levine concludes Hume’s argument that “no one is justified in believing that a miracle occurred, at least not on the basis of testimony, succeed” (p. 296).
Philosopher Nicholas Everitt has a contrasting view. After telling readers a miracle for Hume is a transgression (or violation) of a natural law, he describes Hume’s philosophical argument in Part I as follows:
Unless the evidence in favour of a violation miracle is overwhelming, a rational believer should believe that the miracle did not occur; and that even when the evidence is overwhelming, the rational believer will always suspend judgment, because there will always also be overwhelming evidence that the miracle did not occur. (The Non-Existence of God, p. 114)

The overwhelming evidence that a miracle didn’t occur is to be found in everyday experiences of the uniformity of natural causes and events expressed in natural laws.
Part II of Hume’s argument is a mainly an evidential one, “designed to show that as a matter of historical fact, the evidence for the occurrence of miracles is never overwhelming. If that is true, there will clearly never be no good argument to be drawn from the occurrence of miracles to the existence of God.” (p. 114).
The big disagreement between Everitt and Levine has to do with the strength of the two parts of Hume’s essay: “The real destructive power of Hume’s critique lies in his philosophical argument” says Everitt, “that even in the most favorable circumstances possible (favourable, that is, to a belief in theism) it would not be rational to believe that a miracle occurred.” (p. 116) Then this: “His historical evidence that these most favourable circumstances have never in fact occurred is comparatively unimportant: even if it were wholly controverted, his main argument would remain unaffected.” So he says, ‘we can ignore that part of his discussion here, as it depends on the truth of historical rather than philosophical claims.” (p.116). In his favor his critique is philosophical in nature, not historical, but there certainly are philosophical issues involved in Part II of Hume’s essay that deserved his comments. So I can only conclude Everitt thinks the argument of Hume in Part I does all the work for him.
Everitt argues that “since a miracle is by definition a violation of a law of nature, it is maximally improbable. So, if testimony in favour of a miracle is to be rationally credible…it must hugely strong testimony—if fact, maximally strong. But even if the testimony were to achieve maximal strength, it would all be cancelled out by the antecedent improbability of anything which contravenes the laws of nature…and since the net evidence would be zero (maximal evidence for is cancelled by maximal evidence against), the rational response would be non-belief in the occurrence of the supposed miracle.” (pp.115-116).
Everitt clarifies:
Hume’s conclusion does not imply that levitation is impossible, nor that testimony that it has occurred is always incredible. His conclusion is that the more credible the evidence that levitation has occurred, the less we are justified in believing that levitation is contrary to the laws of nature, and hence the less we are justified in believing that levitation is a violation miracle.” (p.117)

So let me put it to my readers. What would it take for you to believe a miracle had taken place given natural law and the fact you have never previously experienced a miracle nor anyone else you know (that is true, right?) What kind of miracle would it have to be? Let’s say one day a man’s arm was blown off and the next day it had regrown. It’s never going to happen, that’s for sure. If someone claimed it did, would you believe it was a magic trick of some kind? How about a virgin having a baby without any male sperm? How about someone telling you s/he heard god’s voice? What about YOUR hearing a god’s voice? What of someone coming back to life after being embalmed at the morgue?