This poem sounds like the surface of a weathered tombstone. This smooth rough feeling comes from a poem that doesn't use big fancy words or seek out the prettiest words possible. This poem says what it means to say because it doesn't have the space to spare, and its distilled truth, unhindered by flowery language, is part of what makes it so effective.
All of the language is simple, and the only word longer than two syllables is in the title, "epitaph." Sound-wise, though, that title sets us up for a remarkable case of assonance, in which the short E sound of epitaph echoes consistently throughout the poem, as in "depths" (2), "trembled" (4), and finally with the last word, "dead" (6).
What's to be made of this sonic repetition? Well, just as life and death are connected in joy and sorrow, the sounds of this poem connect it, beginning to end. The repetition is simple, yet profound, fitting for a statement that could be printed on a gravestone. The assonance in this poem reminds our ear, though, that death is not an ending, but an opportunity to see (and hear) connections to life.