1. And the meeting house windows, blank and bare, / Gaze at him with a spectral glare.
This is a couplet. You can tell this because there are two lines, a couple, as indicated by the slash between the phrases, as well as the end words rhyming.
2. A glimmer, and then a gleam of light / He springs to the saddle, the bridle he turns / But lingers and gazes, till full on his sight / A second lamp in the belfry burns.
This excerpt, I believe, is meant to highlight the end rhymes. You see, in the first and third lines, the last words rhyme, and the second and fourth lines' last words rhyme.
3. ...the Mystic meeting...
Seeing as how this is so incredibly short, and both "mystic" and "meeting" start with an "m", it is safe to assume that this is meant to highlight an alliteration. An alliteration is when two or more words in a row start with the same letter. A famous alliteration is in the tongue twister, "she sells seashells by the sea shore."
4. ...like a sentinel's thread / The watchful night wind...
This is a simile. Both similes and metaphors compare one thing to something generally more abstract in order to describe it better. In order to tell if something is a simile or a metaphor is to look for the words "like" or "as," because those are used in similes, but not metaphors. Since this uses the word "like," it is safe to assume that this is a simile.
