My long two-pointed ladder's sticking through a tree Toward heaven still, (lines 1-2)
The beginning of the poem sets the stage for a kind of double-reality. On the one hand, we have a conventional image of a ladder in a tree – what could be more commonplace than that? But the addition of "toward heaven" gives the poem religious overtones and alludes to the story of Jacob's ladder in the Book of Genesis. We wonder if the ladder merely points toward heaven, or if it actually ascends heaven, like the ladder in the Biblical story.
Essence of winter sleep is on the night, The scent of apples: I am drowsing off. (lines 7-8)
For the first time we start to think that maybe he is not narrating the poem from the orchard, while standing on the ladder. The revelation that these confused thoughts occur as the speaker falls asleep will cover the rest of the poem, and it even makes you go back to the beginning to reevaluate earlier lines. It's kind of like the movie Memento, in which past and present memories intertwine.
And held against the world of hoary grass. It melted, and I let it fall and break. (lines 12-13)
This poem has different "lenses," like when you wear crazy sunglasses with different kinds of colors. Or like those Kanye West sunglasses with the bars over them. So far we have the "lens" of the speaker's sleepiness, and now he adds another lens – the "strangeness" that has covered his vision all day, ever since he looked through a sheet of ice that morning.
Magnified apples appear and disappear, (line 18)
This line illustrates a problem in interpreting the poem: many of the images could be ascribed either to dreaming, to memories from earlier in the day, or to present events. The speaker seems to be having an after-vision of apples, having stared at them all day.
The woodchuck could say whether it's like his Long sleep, as I describe its coming on, (lines 40-41)
Although in a normal waking state he would know perfectly well that the only kind of sleep he can have, as a human, is "human sleep," in his drowsiness he hovers on the edge of another kind of reality. He almost thinks he could be like a woodchuck who hibernates through the whole winter. A "long sleep" could also be a symbol for death.