Context

Macbeth has just been told that his wife is dead. Far from breaking down, he delivers a soliloquy of devastating philosophical detachment, finding life itself to be a meaningless succession of identical days.

How the repetition works

Diacope — broad-form epizeuxis with a short connective (here, “and” or “the”) between the repeated words. About this distinction →

The triple "tomorrow" makes the future feel monotonous before it has even arrived. Each repetition adds not anticipation but identical, weary continuance. The repetition enacts the "petty pace" it describes — three tomorrows that creep, syllable by syllable, with nothing distinguishing one from the next.