The hewn trees are a warning of what happens to people who have dealings with the devil. They are inscribed with the names of soulless people. The devil, whom Tom meets here, informs him that he uses these trees for firewood, suggesting that those who get involved with the devil burn in hellfire.

Tom's new house and his churchgoing habits reveal his hypocrisy. The more he does the work of the devil as a money lender, the more he does not want to expose what kind of person he really is. The fact that he lives in a house that looks grand on the outside while unfinished on the inside indicates that greed drives him: he wants money only for the sake of money. Inside, he is empty.

Tom also pretends to be a pious Christian of the type that persecutes others in the hopes it will keep him from the devil's snares, but his soul is too hardened to respond to the true message of Christianity. All of this imagery repels readers and convinces us that we don't want to be like Tom.

Throughout "The Devil and Tom Walker," Washington Irving uses a highly descriptive style of writing to great effect. The first of these images is largely about creating a sense of place. Walker's encounters with the Devil play out in the wilderness, beyond the reach of civilization. These descriptions achieve much in setting the stage for those later interactions.

The imagery of the hewn trees conveys a sense of the otherworldly and supernatural. Here, the trees are representative of real people, with their rotting condition signifying corruption. Furthermore, we must also contend with the image of Old Scratch himself. His presence among the trees points toward his influence in human affairs (an influence that people may not be entirely aware of).

The last two images reveal aspects of Tom Walker's own characterization. The description of the house emphasizes his greed and miserliness. From the story's very beginning, that miserly quality has been one of his defining characteristics. As we can see in the image of the house, very little seems to have changed on that account.

Finally, the imagery involving Tom's religious life serves to advance a sense of his own spiritual crisis, created from an awareness of his own eventual damnation. Walker has made a deal with the Devil and is well aware of what he has done. However, this does not mean that he is comfortable with his own allotted fate. Thus, his displays of religious fervor are closely linked to a deeper underlying anxiety as to his own future and the costs that will be exacted upon him.

Characterization can be defined as the process of "fleshing out" a character by giving details about its thoughts, behaviors, physical qualities, motivations, and other features which contribute to the illusion that the character is real.

Mood is the feeling or other emotional sense that the reader is intended to have based on certain details. 

• The details describing the swamp are establishing a "gloomy" mood - the trees are specifically described as gloomy, and this is substantiated by the swamp being dark at midday. The swamp is also characterized as treacherous, in that is "betrays" the traveler into puddles of mud. 
• The hewn trees are meant to represent individuals, and their presence may serve both to set the mood as one of foreboding (in that their fate is tied to that of the tree, or perhaps vice versa - the "magic" at work here is unclear) and the condition of the trees serves to characterize the people they represent - all variously scored by an axe, suggesting the impact of their sins, as well as trees that are rotting (corrupted) and fallen (dead).
• Tom's new house characterizes him as a superficial braggart, yet simultaneously miserly - he somehow manages to combine some of the worst traits possible. This is probably intended to establish a mood of disgust - not only are we displeased by Tom's showboating, but by the blatant underlying selfishness of his motivations.
• Tom's churchgoing phase further characterizes him as short-sighted and selfish. The mood here is probably one of annoyance - both at Tom's sudden conversion to a man of faith, and at his clear misunderstanding of how faith works, and that it is not about making a show of himself.