Adam and Eve did not sin they 'became like' their creators, i.e. no longer naive. Letting the author explain his very short story leads to a very different conclusion than the countless spins theologians have overlain upon it. Unfortunately, we primarily know of this particular legend only through the voice of one such theologian (P).
Appreciating the literary stages the Genesis composition passed through prevents anyone from being dogmatic about the original purpose the small more ancient elements individually had, prior to being woven together. However in this case the original intent seems to be retained by the "become like one of us, knowing good and bad". IOW, the end of childlike naivety.
The P compiler/redactor, that borrowed this snippet, seems to have in mind the Eden ideal of 'holy place' with it's implied connections to the temple rights that he and his fellows were engaged in. The place seems to be of greater import than the message. Some of this is lost on modern readers as a result of the merging with other traditions in the later centuries BCE.
So what we have is a snippet of metaphor drawn from local cult of the goddess brilliantly commandeered to emphasize the naivety of man in contrast to the creators, preserved in a larger narrative (P) that utilizes it to contrast sacred from profane then later merged with other traditions into a collection, more concerned with preservation of legends, loosely woven into a 'history of man' (R/sages).