Do you mean the poem? If so, note that the conflict concerns a woman who is tempted to forsake husband and child, hearth and home, to run away with a man she is infatuated with.
It was a common folk belief of the time that Satan could never disguise himself completely but had to reveal some body part portraying him for who he really was. (Kind of a "rule" in the game of deception.) Thus, he is often shown with horn, a hoof, a tail or something unnatural. That way the temptation was at least "fair play."
Note that running away to sea is a universal symbol in itself of escapism or the desire for emancipation. It also symbolises the desire for new experiences and absolute freedom.
In 1945 Elizabeth Bowen had a short story published inspired by this medieval poem. Check out the site below for symbolism in this work and the correlation between it and the original poem. Note that this is a source where not all information is verifiable since its information is contributed by the general public.