The Healing of the Nations

Revelation 22 two says a tree of life grew on each side of the main street. The leaves were used for medicine to hill the nations. Teresa asks if by this point we would be in new heaven and new earth, or even just heaven in general, why would there be a need for medicine? We have to remember this is a metaphor,. It's not about curing some literal ailment. Rather, the healing here is metaphorical of the nations.