In the icy air of night! (line 5)
One thing you might not notice immediately about this poem is that each of the sections takes place at night. In a way, the nighttime is almost like a character in the poem. Nighttime is a thread that holds the whole thing together. In this first section, the night is full of happy glittering stars, and everything seems peaceful. Still (and maybe we're just imagining it because we know what's coming), isn't there something a little sinister about that "icy air"?
While the stars that oversprinkleAll the heavens, seem to twinkle (lines 6-7)
The stars in this first section twinkle right along with the bells. In the first two chunks of this poem, everything is in harmony. The manmade bells and the natural world sing in tune, and everything is just fine.
To the turtle-dove that listens, while she gloatsOn the moon! (line 23-24)
With the exception of the ghouls that show up later, this is the only living thing in the poem that we get a close look at. The turtle-dove is an old symbol of true love and fidelity. That makes her just the right choice for this happy part of the poem. The loving looks that she is giving the moon are important too. Remember, the whole point here is that love and happiness and harmony are everywhere, even in birds and the moon.