There is an implicit aspect to this story which was pretty obvious to any ancient hearer/reader familiar with mythology but is often missed by modern readers with a monotheistic or humanist backgroud: Eden was Yhwh's garden (cf. 13:10), a "garden of gods" (probable first sense of the plural gan-'elohim in Ezekiel 28:13; 31:8f; whence the plural in Genesis 3:22 which is a vestige of the original polytheistic setting of the story). The garden was not planted for mankind but for the gods. Like in most ancient creation myths mankind is not created for its own sake but to serve the gods*, in that particular case in a gardener's office (2:15, "to till it and keep it"). Which means that both the tree of knowledge and the tree of life are god food, much like nectar and ambrosia. From such a theocentric perspective the story makes much more sense than from the anthropocentric one which is so natural to us.
* E.g. 'Enuma `elish, t. VI l. 1-10:
When Marduk heard the words of the gods,
His heart prompted him to fashion artful works.
Opening his mouth, he addressed Ea
To impart the plan he had conceived in his heart:
"I will take blood and fashion bone.
I will establish a savage, ‘man’ shall be his name.
truly, savage-man I will create.
He shall be charged with the service of the gods
That they might be at ease!The ways of the gods I will artfully alter. (