One of the reasons why this poem can be difficult to get through is because Coleridge purposefully mixes up his symbols. He's not trying to make things difficult on purpose, though it may feel like it at times. Instead, he's trying very hard to demonstrate just how mixed-up the real world can be. He does this through lots of ambiguity—meaning he gives us a symbol of something good and then pairs it right away with something not so good. The idea is that the world is not just black and white. Coleridge wants to keep us lingering in that weird shady grey area, where there are few direct answers. We have to admit that he's done a pretty good job of keeping us spinning around in places.
Line 2: Owls and cocks are bird versions of Bert and Ernie—they are polar opposites. Owls are night birds and birds of prey. Roosters are day birds and basically scavengers (or moochers if you think like a farmer). Owls are also wild, while cocks are generally domesticated.
Line 7: A mastiff is a gigantic dog, and can be fairly frightening. They aren't particularly aggressive, but they do not take kindly to someone threatening their territories or their masters. Because of their role as a guard dog and because of their massive size, they are often thought of as masculine. However, Coleridge cuts this awesome animal down to size by telling us that it's female, old, and toothless. This dog is the very epitome of having a bark worse than its bite.
Lines 14-15: Chilly and dark is spooky, but the narrator assures us that it's only chilly, not dark. So, again, this is not a complete submission to evil, just a partial one.
Lines 16-17: It's cloudy, but still clear enough to see the moon. The weather is very much a "could be worse!" kind of situation.
Lines18-19: The moon is full, which could be nice and eerie, but, no, she's still small and dull.
Lines 21-22: Oh boy, it's spring! Wait. No, it's still cold outside—bummer.
Line 30: Using the word "lover" creates a feeling of intimacy in the relationship between Christabel and her betrothed knight. However, he's also far away, which creates both a physical and emotional distance.
Lines 49-52: This one last leaf reminds us that the story is taking place in that weird place of seasonal transition when the calendar says it's spring, but the weather and the trees say it's still winter.
Lines 58-68: This whole stanza is full of back and forth symbols. The lady is frightening, but she's dressed in the purest of white. She has a stately air about her, indicating that she's probably a noble, like Christabel, but her arms and neck are bare, which is a little shocking for a woman during this period of time and, well, because it's cold.
Lines 71-72: The narrator calls the lady strange, but then in the very next line we learn that her voice is soft and sweet, which is unexpected.
Lines 129-134: First the lady is in pain, and then she isn't. The ambiguity here is to call attention to the threshold and how it affects Geraldine. There's more to meet the eye here than a quick fall and her leaping up shouting, "I'm fine!"
Lines 147-148: The evil isn't strong enough to wake the dog up, but it is definitely there in a gentle scent because the dog begins to growl in her sleep.
Lines 163-165: The shields and weapons of Sir Leoline tell us that he is a seasoned warrior, a contender. However, Christabel lets us know that he does not sleep well, so maybe he's not such a tough guy after all.
Line 171: Death is dead, so he wouldn't breathe much, right? That makes us wonder how exactly death would be stifling a breath in the first place. Obviously, death is just very nearly dead, but not quite dead yet.
Lines 175-177: This one really makes our heads spin! First the moon shines, then it doesn't shine in the room at all, but then we're told that Christabel and Geraldine can see just fine anyway. Whew. Perhaps this reflects Geraldine's thoughts as she moves back and forth from the thoughts of a lady to the thoughts of a witch.
Lines 178-181: Here the narrator gives in and admits that there's some weirdness happening. Christabel is sweet and innocent, but for some reason she has creepy carvings all over her room. Whose idea was that? Her bedroom gives us a hint that maybe Christabel isn't 100% sweet and innocent either. Maybe Geraldine doesn't have to be completely evil to seduce the young woman.
Lines 292-293: Sleeping and dreaming with open eyes is, um, not normal. What the narrator is trying to say is that he saw everything clearly, but he thought he was dreaming because what he saw was just too scary and weird.
Line 302: In many ways, it is this line that is the mother of all ambiguous statements in the poem. It really helps us grasp the point of all the weird wishy-washy, back-and-forth commentary. On one hand, we can see the star as the sun and it seems that simply a night has passed by. However, what this setting and rising star represents is death and birth. Christabel as a whole is a bit of a symbol here, since she herself exists in this place of both birth and death (seeing as her mother died while giving birth to her). Now, however, she experiences yet another death and birth—the death of her innocence and the birth of her sin. This scene is further illustrated if we look back to the last three lines of the previous stanza (299-301) and see that the speaker likens Geraldine to a mother with her child in her arms when she's holding Christabel as they both sleep. A little later, in line 318, the narrator again uses the metaphor of an infant to describe her. Geraldine has given birth to Christabel's dark self—yipes.
Lines 313-319: Christabel is at once relaxed and upset. She is crying, but she also smiles. She's obviously struggling with this new version of herself. Perhaps she feels relieved to let her true colors shine through. At the same time, she still struggles with the feeling that being with Geraldine is wrong, according to what she has been taught her entire life.
Lines 352-359: Sextons, though their titles may make us giggle a bit, are not particularly sinful. It's quite the opposite, really, since they are meant to take care of the church. They aren't holy men, but, generally speaking, the church isn't interested in letting overly sinful folks take care of their business. Beyond their sin is the fact that these particular sextons are dead. Still, they're able to add to the ringing of the bells every morning. This presence of both life and death reminds us that Sir Leoline has created a serious downer of an environment for all of his people by reminding everyone of their mortality (and the mortality of their loved ones) every morning. The people exist in a strange place where they are all still alive, but it's difficult to live life joyfully or gratefully when visions of the Grim Reaper are painted for you every single day when you wake up—eesh.