Calvin takes as given the historicity of Adam and Eve and the events surrounding their creation and fall. He rebukes, on this score, the 3rd century theologian Origen and "others like him" who -- finding little of value in Adam and Eve's historical personages -- "took refuge" in allegorical interpretation of the early chapters of Genesis. Such interpretation generally discovered nothing but moral(istic) import (in medieval technical terms, a tropological meaning) in the events depicted in these chapters.
Yet Calvin has no qualms whatsoever about discerning in our first parents' rebellion and God's response to the same a pattern which finds expression in every subsequent generation of rebels-without-good-cause doing their rebel thing against God. In other words, a careful consideration of Adam's sin and God's response to it has much to teach us not only about Adam's sin and God's response to it, but also about our own sin, our efforts to evade culpability for sin, and God's work of exposing sin for what it is and then dealing with it far more effectively that we ever could.
What might we learn from Adam's response to his own sin? We learn something about our persistent efforts to evade responsibility for what we've done and, when such evasion proves unsuccessful, to make satisfaction for our guilt on our own terms.
Efforts to evade culpability for sin generally involve a fair bit of finger-pointing at others. Thus Adam points his finger first of all at God and tries to blame him for his dire situation. Discovered by God in the garden (vs. 9) after trying to hide himself among the trees (vs. 8), Adam names his nakedness, rather than his crime, as the reason for his reluctance to face God. It was, of course, God himself who created Adam "starkers" (as my wife would say); thus, Adam's naming of his nudity as the source of his shame was essentially an attempt on his part to "transfer to God the charge which he ought to have brought against himself." It was, in other words, an effort to root "the origin of evil in nature," and so to make God -- the author of nature -- morally responsible for Adam's shame and everything which informed it.
When asked more pointedly whether he had broken God's commandment (vs. 11), Adam merely doubles down in the blame game, simultaneously putting forward "his wife as the guilty party in his place" and advancing yet another "accusation against God," inasmuch as Eve "had been given [to him] by God." Eve, for her part, learns a quick lesson from Adam: "[Eve] is not struck dumb" (as she should have been by the gravity of her guilt), "but, after the example of her husband, transfers the charge to another; by laying the blame on the serpent she foolishly, and indeed impiously, thinks herself absolved."
So it goes with each of us: "We also, trained in the same school of original sin, are too ready to resort to subterfuges of the same kind," ultimately daring even to blame God for the sinful desires which we indulge. But our own finger-pointing is "to no purpose," Calvin reminds us, "for however much incitements and instigations from other quarters may impel us, yet the unbelief which seduces us from obedience to God is within us; the pride which brings forth contempt is within."
Even more futile than Adam's attempts to evade culpability is his effort to deal with his shame by cloaking himself with "a girdle of [fig] leaves." "There is none of us," Calvin comments, "who does not smile at [such] folly, since, certainly, it was ridiculous to place such a covering before the eyes of God."
Yet our own efforts to deal with our guilt often prove more laughable than Adam's. Calvin insightfully identifies the simple passage of time as one of the more flimsy cloaks we seek to cast over our sin and culpability. The more minutes, hours, and days that intervene between us and our transgressions, the less we feel the sting of guilt for what we've done. And so we delude ourselves into thinking that God, like our own forgetful consciences, is actually appeased by time. "By an oblivion of three days' duration, we imagine that we are well covered." Unfortunately for our delusion, God transcends time, and so our criminal actions and our guilt are ever present (tense) to him. Time may heal certain wounds between human parties, but before God, time proves just a futile as a pair of fig-leaf undies for covering our guilt.
From God's response to Adam's sin we gain insight into what God continually does with sin (and, in that process, sinners), first naming it for what it really is, and then dealing with it through the atoning work of his own Son.
Calvin discerns a two-part movement in God's response to Adam's sin; God first convicts Adam, and then consoles Adam. God convicts Adam by coming "nearer" to him and -- both literally and metaphorically -- drawing him out, "however unwilling and resisting," from "the tangled thicket of trees" where he has hidden himself. The exposure of Adam ultimately consists in God's reminder to him of that single explicit command given to him when the garden of delights was entrusted to his care.
Thus God's commandments ever serve to convict sinners of their guilt: "In the same manner we also are alarmed at the voice of God, as soon as his Law sounds in our ears." In most cases, of course, genuine admission of guilt requires sustained exposure to God's Law. "We snatch at shadows, until he, calling upon us more vehemently, compels us to come forward, arraigned at his tribunal."
Having humbled and convicted Adam by means of his Law, God consoles Adam with the good news of One who would come to reverse the fall and its catastrophic consequences, and through his perfect obedience to God's Law and suffering for sin provide a covering far more substantial than fig leaves for Adam's guilt and shame; a covering, indeed, which God himself would prove unwilling and unable to penetrate with his gaze. God consoles Adam, in other words, with the promise of Jesus Christ, God incarnate, who in due course would fulfill God's law and suffer death in the stead of Adam, Eve, and every subsequent sinner willing to place his or her confidence solely in him.
Jesus Christ was named rather obscurely to Adam and Eve (in the midst of God's rebuke of the Serpent) as "the seed of the woman" who one day would crush the Serpent's head (vs. 15). "Certainly in that [promise] the remission of sins and the grace of eternal salvation is contained." The precise woman in view in this prophetic text is not, Calvin argues, the Virgin Mary (contra Roman interpretation), but Eve, who "being first deceived... had peculiar need of consolation."
The "seed" who would triumph over sin and all its consequences is, of course, Jesus Christ, who crushes the Serpent's head in his death and resurrection. But it is not him alone. Noting the collective sense of the word "seed" (i.e., descendants), Calvin discovers in Genesis 3.15 an additional promise that every believer who joins himself or herself to Christ will, in him, equally triumph over the Serpent (and so over sin, death, and hell), and thus be restored to eternal fellowship with God. Genesis 3.15 contains, then, nothing short of the promise of one whose work would eradicate the guilt and shame of every person willing to take off his or her fig leaves and put on the perfect righteousness of Jesus Christ.
In sum, while Adam is, according to Calvin, a genuine historical person, there is also a genuine sense in which Adam constitutes a symbol of every man (and woman). Adam's sin and God's response to it serve as a (prophetic) picture of every individual's response to his or her guilt and God's own, more radical response - namely, that of bringing the sinner to the depths of despair by confronting him or her with his Law, only to raise the sinner to the highest peaks of hope by consoling him or her with the Gospel of Jesus Christ and his sin-atoning work.