"Rappaccini's Daughter" can be read as an allegorical representation of the biblical Fall of Man. Rappaccini's garden resembles the Garden of Eden in many ways: it is a beautiful and bountiful garden, populated by one man and one woman—that is, Giovanni and Beatrice. In the biblical narrative, Eve tempts Adam into sin by eating the forbidden fruit. Likewise, Giovanni succumbs to the temptation of Beatrice's beauty and becomes poisonous himself.
However, "Rappaccini's Daughter" turns this story on its head by shifting responsibility for the Fall from Eve to Adam: it is Giovanni's failure to resist his curiosity about Beatrice that provokes his downfall, and it is his reliance on reason rather than intuition that subjects the innocent Beatrice to undeserved pain. Beatrice's final suggestion that there was "more poison" in Giovanni than in herself cements the notion that Giovanni is responsible for the Fall, not Beatrice.
It is notable that the narrator makes explicit reference to the story of Adam and Eve early in the story when Giovanni watches Rappaccini tending to his garden, though the story presents Rappaccini (not Giovanni) as Adam:
Was this garden, then, the Eden of the present world? And this man, with such a perception of harm in what his own hands caused to grow—was he the Adam?
The fact that the narrator presents this comparison as question suggests that Giovanni, not Rappaccini, is actually the one who's comparable to Adam—but he doesn't know this yet. This foreshadows the ending of story, in which, like Adam (who succumbs to his curiosity), Giovanni sparks his own downfall.