What is the importance of the Garden in the novel, This Is How You Lose the Time War?

The Garden is the area and society that Blue is from. It is depicted as the polar opposite of the Agency both in geography and lifestyle -- it is overrun by nature. The people that are born into the Garden, like Blue herself, are able to shapeshift or somehow embody things in nature. When Red tries to go there late in the novel in order to help Blue by giving her poison to protect her future body from it, she finds that the atmosphere is incredibly hostile to her, a member of the Agency. All the bugs there hurt her skin simply with their wings or other appendages. It is basically one of the two reactions to the future that we see humans take in the novel, which is to fuse ever closer to the natural world.