Possible explanations for some of the religious symbolism
The River Bank seems similar to the Garden of Eden. Its inhabitants are all animals who lead mostly conflict-free pastoral lives with no unwholesome passions, no threat of mortality, and almost no change. Instead of Adam and Eve, the main characters who make their abode in the River Bank are the Water Rat and the Mole, who exhibit something of a masculine/feminine dichotomy if one looks carefully at their interactions. Combine this state of suffused bliss with the close proximity of the god of nature, and you have a perfect representation of Eden.By contrast, the Wild Wood, which lies just beyond the River Bank, is fraught with danger; when Adam and Eve sinned, Jehovah cast them into the wilderness, as he did Lilith when she refused to submit to Adam. The deep, dark wilderness is the home of demons and the stout-hearted animals who can best them (like the gruff but noble Badger). That said, the weasels are not beyond redemption, as we see in the final chapter. Perhaps animals are born without original sin.
Finally, we come to the Wide World, presented to us as man's world. This godless tableau is where Toad (significantly, the story's only major non-mammal character, wearing the form most suited to cursed princes) spends most of his time. He errs in pursuing worldly interests: seeking pleasure through material gain and fast living as well as singing his own praises. These are all classic sins, but he too can attain redemption, as his friends' attempts to save him from himself attest. Whether they succeed is up to the reader, really.
It should be noted that the book is likely an exercise in Applicability rather than direct allegory (especially since it seems to have influenced Tolkien, although the similar values could just be a coincidence).
