The nature of the question is very broad. You might see this moved to the "Discussions" section because so many will have many different takes on this. In my mind, one of the most intense highlights is the thematic development of how construction and destruction are closely linked. Shelley's work is powerful because it highlights how the powers of construction and the ability to create lie so very close to the ability to destroy and cause pain and suffering. I think that this is developed in both Victor and the monster. Both of them represent this theme in different ways. In doing so, Shelley brings out the complexity in what was previously seen as a binary dualism. The ambiguity and ability to perceive that which is complex is one of the highlights of the novel. It is one that helps to describe the modern setting with advances in science and industrialization taking place in Europe and, eventually, all over the world. Shelley's development of this theme has to serve as one of the novel's highlights because it becomes so vital in both its understanding and the modern setting, in general.
Chapter 12 focuses on the loss of innocence, in regards to the daemon. The most important theme which is explored, not only in these two chapters but the entire novel is that of the dangers of knowledge.
All of Walton, Frankenstein and the creature are all alien in their society, whether it be by choice (with Walton and Frankenstein) or due to a deviant appearance (with the monster/daemon). This thereby leads to the reader acknowledging the concept that people are scared of the alien, the unknown, and this causes them to have a negative approach towards it, therefore making the thing more likely to respond negatively.
The two chapters focus on the theme of good vs. evil.
The reader is baffled with considering whether the daemon is really 'evil' when he talks in chapter 13 of his true desire, even necessity for a loved one, someone to appreciate him. Whereas, Frankenstein is on the borderline of good, as the reader interprets that he really isn't a heroic, nor is he a particularly desirable person, due to his mistake in creating a monster that is omnipotent, and therefore causes a power shift between creator and creation.
The reader is reminded of the daemons great power and inhumane qualities when he becomes "lost among the undulations of the sea of ice". The reader can almost imagine in their mind just how chilling and inhumane this context is, in which the daemon is not at all troubled.
The fact that the daemon was walking through a sea of ice, also suggests his permanence, and thereby his strength no matter how much time pasts (alike to ice). Nothing can truly harm him physically, besides himself.
In comparison to the daemon, Frankenstein appears very much weak and incapable "...my heart was heavy, and my steps slow." This also metaphorically reflects upon Frankenstein- as he is incapable, also, of escaping the happenings of his life.
This reinforces the idea that the ability to depict omnipotence and omniscience is not necessarily as great as first deemed to be- even when seemingly you are in power, things can easily reverse. You never know what's going to happen next.
That's just about all I can think of... hope it helps at least somewhat! :)