Eating from the tree of life was a "transgression", not a sin. They were taught to see what was good and what was evil, and now given a choice between the two. The question is, was man perfect in the eyes of God before the transgression. I believe he wasn't. He was still a part of decaying matter in a decaying world. He was being lied to (by a demiurge) to do the will of his creator under ignorance.
Christ, through the Father, saw the truth, and used the serpent to coax Eve to eat, thus causing man to see the reality. When the demiurge's hand was shown, he admitted the death, and Christ now intervened to save mankind.
As the OT is full of a demiurge and the Holy Spirit showing man the truth, it wasn't until Christ came in the flesh, that we understood the real truth.
"But what they call the tree of knowledge of good and evil, which is the Epinoia of the light, they stayed in front of it in order that he (Adam) might not look up to his fullness and recognize the nakedness of his shamefulness. But it was I who brought about that they ate."
And to I said to the savior, "Lord, was it not the serpent that taught Adam to eat?" The savior smiled and said, "The serpent taught them to eat from wickedness of begetting, lust, (and) destruction, that he (Adam) might be useful to him. And he (Adam) knew that he was disobedient to him (the chief archon) due to light of the Epinoia which is in him, which made him more correct in his thinking than the chief archon. And (the latter) wanted to bring about the power which he himself had given him. And he brought a forgetfulness over Adam."-Apocryphon of John