Stanza 3 Summary

Lines 24-27

But O! how oft,
How oft, at school, with most believing mind,
Presageful, have I gazed upon the bars,
To watch that fluttering stranger!

• Coleridge switches to a new stanza here, because he's finished with contemplating how the film (or "stranger" as people in Coleridge' time called it) mimics his own mind. Now, he's going into a reverie, remembering how he used to stare at the "stranger" that would form in his classroom's fireplace, back when he attended school as a kid (that would have been Christ's Hospital School, in London).
• The "stranger" is "presageful" (able to tell the future), since it was believed to predict the arrival of an unexpected guest. Coleridge is hoping someone will arrive to rupture his boredom—he loved to daydream and zone out. 
• Notice that this stanza begins with an apostrophe, "But O! how oft," before repeating "How oft." It breaks the blank verse meter, before jumping right back into it.

Lines 27-31

[…] and as oft
With unclosed lids, already had I dreamt
Of my sweet birth-place, and the old church-tower,
Whose bells, the poor man's only music, rang
From morn to evening, all the hot Fair-day,

• As a kid in school, Coleridge says that he would imagine his birthplace—Ottery St. Mary, in southwest England, far away from the hustle-and-bustle of London's metropolis—where he used to listen to the church bells on Fair Days. 
• The church bells—described as "the poor man's only music," since the music they make is totally free—are similar to the "stranger" in that they're a harbinger of a better time to come.
• Also, Coleridge's lids are "unclosed" because he's daydreaming—he's not actually sleeping in school.

Lines 32-34

So sweetly, that they stirred and haunted me
With a wild pleasure, falling on mine ear
Most like articulate sounds of things to come!

• Even though church bells don't actually speak in any language, their sounds are like "articulate sounds"—they seem to be saying something, maybe better than words could. They talk about "things to come"—which might refer to the afterlife, the Kingdom of God, or simply a more spiritual life. 
• They're similar to the "stranger," since the bells are also predicting some unknown and probably welcome event. 
• Coleridge, as he remembers himself, feels overjoyed at this point.

Lines 35-36

So gazed I, till the soothing things, I dreamt,
Lulled me to sleep, and sleep prolonged my dreams!

• Coleridge ends up getting carried away by this reverie—soothed and comforted—until he falls asleep later in the evening. (This is still the child Coleridge, not the adult Coleridge, who is sitting up at night and remembering this.) Sleep helps him continue to have these pleasant dreams about his past in the countryside and about nice things that might happen in the future. 
• This all feeds into Coleridge's reputation as a dreamer with his head in the clouds (which might not be entirely justified, though he's playing right into it).

Lines 37-39

And so I brooded all the following morn,
Awed by the stern preceptor's face, mine eye
Fixed with mock study on my swimming book:

• Kid Coleridge zones out the next day in class, too. He pretends to read, to avoid getting into trouble with his "stern preceptor" (that would be the headmaster, James Boyer, who apparently loved to beat kids). 
• The book itself isn't actually "swimming"—Coleridge's vision is, because he's still sleepy and dazed. 
• Is it just us, or does this seem like a pretty long time to be fantasizing about unexpected good things, brought by church bells and films of soot? 

Lines 40-44

Save if the door half opened, and I snatched
A hasty glance, and still my heart leaped up,
For still I hoped to see the stranger's face,
Townsman, or aunt, or sister more beloved,
My play-mate when we both were clothed alike!

• Interestingly, the "stranger" Coleridge is waiting for isn't a genuine stranger—it's someone he knows, like a person from his hometown, an aunt, or his sister. 
• He's showing some nostalgia for the good old days, before he was toiling away at this lousy school. The fact that he and his sister "were clothed alike" indicates that these days were simple. They hadn't yet been differentiated into different roles, and could experience life in a more unified way. 
• In a sense, this suggests that the promises made by the church bells—of some coming good—are also heralding the arrival of a presence that might be strangely familiar. Could it be… God? (Coleridge might have something to say on that question, later in the poem. We'll just have to keep reading…)