Genesis2:9

Usually this would mean “the tree that gives life.” However, God had already given them life, so the fruit of this tree could not give life in the sense of initiating life; the only way it could “give life” would be to “sustain life,” which is what I think is intended here. Maybe the fruit of this one tree gave them everything they needed in the way of nutrition, which was later supplied by working the ground. After the fall, a diet made up of only fruit would be lacking in certain key nutritional elements, so, although we are not told specifically, it is logical to think that this tree called the Tree of Life, would supply what was otherwise lacking, and thus grant continuation of life. If this is true two more things could also be logically assumed: 1) that continual eating of this fruit was required in order to live continually, not a single bite as we have often assumed, 2) it is likely that Adam and Eve had already been eating from this tree before they fell into sin. But that was ok because it wasn’t prohibited, and it is likely that it was advisable to eat this fruit to maintain life. (see my note after Gen 3:22 for a fuller discussion on the “tree of life”.)

While the Tree of Life alone provided what was lacking nutritionally in the other fruit trees, the Tree of Knowledge of Good and Evil had the power to provide what was “lacking” (beyond their current knowledge) in moral and spiritual matters. However, God made it clear that such knowledge was not necessary for them, nor was it His plan for them to possess this knowledge. They were not told how it would provide such knowledge, and we now know that it did so through experiencing firsthand the consequences of evil. He placed this possibility within their reach as a test of their trust in Him. It was the only restriction they were given. Notice the balance that is afforded by this method of interpreting the two special trees.