It refers to the Fall, meaning those who eat of the knowledge are then subject to the cycle of life and death, reincarnation. whereas those who remain as enlightened beings have eternal life.
Our physicalness is because of a denseness of existence - fallen state. Unlike the ethereal states of consciousness where one is whole. Our physical evolution has seen us more incarnated. Especially as we are more subject to materalistic reductionism than ever, it's harder to reach those states of wholeness.
Eating of the knowledge refers to not seeing oneself as enlightened or as divine as the source, instead seeing duality and separation - hence our fall into matter.
There is no need to blame the serpent, it is to see the serpent within us, the part that looked outside instead of within.