What do the leaves of the tree of life do for the citizens of the eternal city?
The leaves of the tree of life are therapeutic for the citizens of the eternal city. Eating them enhances their eternalness, much like a daily remedy. Adam was not permitted to eat from this tree, for doing so would have made him live forever. The citizens will eat because God wants this enhancement.
Les teaches that eating the leaves of the tree of life will be a therapeutic thing for the citizens of this eternal abode. He compares it to an apple a day that keeps the doctor away, meaning the leaves will enhance their eternalness. He explains that this is why Adam was not permitted to partake of the tree of life: had Adam eaten of it, he would have lived forever. The whole concept of the tree of life, even here, is therapeutic. Les says we are going to eat of it because it will enhance our eternalness, which is what God wants and what we would want.