The bell seems to be a sea bell, and it pops up in line 430 of "Four Quartets" in "The Dry Salvages." This bell "[m]easures time not our time, rung by the unhurried / Ground swell, a time / Older than the time of chronometers." When you think of the bell, what you really need to think about is the sound of a bell ringing—something totally beyond words, and totally connected to the present moment.
The bell reminds us of a sort of eternal present moment. It also reminds us of the non-abstract world, a world that underlies all of our concepts and anxieties, like those of the "anxious worried women / Lying wake, calculating the future" (435). The sound of the bell, for the speaker, draws together all of time into a single moment. It basically calls us to the "here and now" the same way that the noise of the bird does.
The Bell Timeline
134: "Time and the bell have buried the day"
430-431: "The tolling bell / Measures time not our time"
442-443: "Clangs / The bell"
461: "Clamour of the bell of the last annunciation"
588-589: "Or wherever cannot reach them the sound of the sea bell's / Perpetual angelus"