Actually it will be after the 1000 years. "...and the leaves of the tree were for the healing of the nations" (Revelation 22:2).

There are two types of leaves. One leaf is for medicine (healing). Another type is a leaf that fades. The leaves on the tree of life will not fade.

"And by the river upon the bank thereof, on this side and on that side, shall grow all trees for meat whose leaf shall not fade, neither shall the fruit be consumed: it shall bring forth new fruit according to his months, because their waters they issued out of the sanctuary and the fruit shall be for meat, and the leaf thereof for medicine" (Ezekiel 47:12).

The King James "fade" is the Hebrew "nabel", meaning to sink into foolishness or drop into senselessness.

The leaves of the tree of life will prevent the nations from sinking into foolishness similar to the foolishness exhibited by well-meaning, well-intentioned, but foolish diplomats in today's world.

The nations will break set patterns of thinking, which have been so unsuccessful down through the centuries. "...nation shall not lift up sword against nation, neither shall they learn war any more" (Isaiah 2:4).