Each matin bell, the Baron saith, Knells us back to a world of death. These words Sir Leoline first said, When he rose and found his lady dead: These words Sir Leoline will say Many a morn to his dying day!
And hence the custom and law began That still at dawn the sacristan, Who duly pulls the heavy bell, Five and forty beads must tell Between each stroke—a warning knell, Which not a soul can choose but hear From Bratha Head to Wyndermere.
Sheesh, this Baron guy is a pretty big downer. Apparently the loss of Christabel's mother has left him in a very dark place. He demands to be reminded of his wife's death every morning when he wakes up.
The matin bell is the daily call to morning prayer. The bells were usually rung at daybreak, so they served as an alarm clock for people like Sir Leoline, who didn't need to be up before dawn to milk a cow or clean a chamber pot.
Sir Leoline is so distraught over the death of his wife that he has instated a law that makes sure that everyone in and around his lands will never forget her. That includes himself and Christabel, who wakes up every morning with bells and prayers that might as well say, "Hey y'all. Good morning and such. Oh, yeah, don't forget your mama is dead. Have a nice day!"
Specifically, Sir Leoline's law is that, every morning when the morning prayer is signaled, the sacristan would run through the rosary, saying his prayer, for the length of forty-five beads. ("Sacristan" is another word for the sexton, the guy who takes care of the church, rings the bells, and sometimes even serves as the gravedigger.) The bell would then ring again, and the space of time between would again be filled with the prayer.
The bell represents death and reminds everyone around, "from Bratha Head to Wyndermere," of their mortality (344). The pause in between when the sexton is in prayer represents life. Since everyone is expecting the next bell while pondering this idea of life and death, the whole experience every morning reminds Sir Leoline and his people that we are all just existing in the pauses between death knells—pretty deep and gloomy stuff.
Geography note: Bratha Head and Wyndermere are real places in a region of England then called the Lake Country. They are now part of a national park in the northwestern part of the country called Lake District National Park. The park is very near where Coleridge lived, which was also very near where his good friend and fellow poet William Wordsworth lived.