Even as in autumn leaves detach themselves,⚓✪ now one and now another, till their branch⚓✪ sees all its stripped off clothing on the ground
The season of autumn and the falling of leaves during that time of year is referenced in Cantos III. In autumn, the weather starts to get cooler and the trees begin to lose their leaves and ultimately die, not being able to do anything to stop their fate. The souls at the Gate and Vestibule of Hell are compared to the leaves that fall during the season of autumn because of their inability to determine and control their fate. Leaves that are falling are unwillingly blown by the wind and brought to the ground like the souls waiting to meet their fate. These souls are waiting in the Vestibule of Hell to see their fate that they mainly have no control over.
In Dante’s Inferno, Dante witnesses souls waiting to be told what level of Hell they will be going to. Dante and Virgil make their way across the Acheron River with the boatman Charon while Dante notices condemned souls trying to escape the river and climb into the boat. There is a multitude of souls Dante sees that are all helpless and desperate, just like leaves falling off of trees in the fall. These leaves and trees have to eventually die and in the Inferno, the souls and sinners know they will be going to some level of Hell eventually. They are eager to meet their fate, yet they know it will not be in their favor.
More metaphors by Dante are provided by this website.