In the fourth stanza of "Break, Break, Break," the speaker says that "the tender grace of a day that is dead" will never come back to him, implying a wish to return to the past, along with the knowledge that this is impossible.
Tennyson's poem "Break, Break, Break" expresses one of the poet's major preoccupations: the indifference of nature and the rest of the world in the face of human suffering. The poet lost his one of his dearest friends (Arthur Henry Hallam, who died at the age of twenty-two) and wrote several poems, including this one, mourning that loss. However, as he observes, the sea and the stones, the fisherman's children and the sailor, neither know nor care of his grief.
Time is just as indifferent to the poet's suffering as his surroundings are. Tennyson wishes he could return to a time of "tender grace" when his dear friend was alive, but the entire mood of the poem proclaims this to be an impossibility.