The Question and Answer section for Divine Comedy-I: Inferno is a great resource to ask questions, find answers, and discuss the novel.
Canto Four is focused on the levels in Hell. Dantes is discussing the moral implications of Hell.... what he sees as Christianity's moral failure. One example would be the necessity of baptism before salvation.... the fact that some are forced to...
The shores of the river represent the boundary of Hell.
In the opening lines, the reader immediately becomes aware of Dantes' view of the world. The metaphor of the forest directly contrats the imperfection of the world with the perfection of God and God's paradise.