Here's a long excerpt from the Wikipedia article on him:
The cornerstone of Fromm's humanistic philosophy is his interpretation of the biblical story of Adam and Eve's exile from the Garden of Eden. Drawing on his knowledge of the Talmud, Fromm pointed out that being able to distinguish between good and evil is generally considered to be a virtue, and that biblical scholars generally consider Adam and Eve to have sinned by disobeying God and eating from the Tree of Knowledge. However, departing from traditional religious orthodoxy, Fromm extolled the virtues of humans taking independent action and using reason to establish moral values rather than adhering to authoritarian moral values.That interpretation of the Biblical story actually resonates quite well with my own. If you think of this and the other stories from the Bible on a metaphorical level, its significance as a historical document actually grows -- at least in my eyes. That our earliest ancestors were able to create and transmit through countless generations a story that symbolically captures the moment when humanity achieved consciousness is an amazing possibility to contemplate.
Beyond a simple condemnation of authoritarian value systems, Fromm used the story of Adam and Eve as an allegorical explanation for human biological evolution and existential angst, asserting that when Adam and Eve ate from the Tree of Knowledge, they became aware of themselves as being separate from nature while still being part of it. This is why they felt "naked" and "ashamed": they had evolved into human beings, conscious of themselves, their own mortality, and their powerlessness before the forces of nature and society, and no longer united with the universe as they were in their instinctive, pre-human existence as animals. According to Fromm, the awareness of a disunited human existence is the source of all guilt and shame, and the solution to this existential dichotomy is found in the development of one's uniquely human powers of love and reason.
See also my post The Serpent, the Tree of Knowledge, and Evolution? from last July.