On the shores and lowest slopes of the mountain, on the island but not yet in Purgatory, are the Late Repentant and the Excommunicated. These are souls who converted at the last minute or who died excommunicated from the Catholic church. These souls will eventually enter Purgatory, and eventually climb the mountain to paradise, but they have a longer journey to make.
It's interesting how Dante handles these border cases in the Comedy. What's the status of a death bed conversion? What's the status of a Christian who dies outside of the church?
Dante's vision draws the circle large enough to include these people, even if, as in the case of the excommunicated, they fall outside of extra Ecclesiam nulla salus ("there is no salvation outside the church").
In Canto III there's a wonderful line in this regard:
The church's curse is not the final word,The church's curse is not the final word.
for Everlasting Love may still return,
if hope reveals the slightest hint of green.
I think many of us will find hope in that line.