Why does the poet repeat the word "break" three times?

"Break, Break, Break" is one of the poems that Alfred, Lord Tennyson wrote after the death of his close friend Arthur Henry Hallam. In it, Tennyson expresses the grief that he feels at the loss of his friend. Hallam was also a poet. He and Tennyson spent a lot of time together, and Hallam became engaged to Tennyson's sister Emily. However, Hallam died during a trip to Vienna at the age of 22.
The elegy "Break, Break, Break" is inspired by a lonely seaside vigil. Tennyson uses the word "break" three times to demonstrate the monotony and rhythm of the waves breaking upon the shore, one after another. As he observes the fisherman's boy playing, the sailor lad singing, and the stately ships reaching port, Tennyson laments that he will no longer feel "the touch of a vanished hand" or hear "the sound of a voice that is still." The waves of the sea will continue to beat endlessly against the shore, says Tennyson, but "the tender grace of a day that is dead will never come back to me." In other words, he longs for the days when he could experience the companionship of his friend, but he will never know those times again.
https://www.poetryfoundation.org/poets/alfred-tennyson