"naked shingles of the world...."See in text(Dover Beach)
In this case, “shingles” refers to stones and pebbles, specifically those found along the shore. The image of the “naked shingles of the world” offers a bleak vision of the future when the sea—the Sea of Faith, that is—has fully retreated, leaving the shores of the world barren.
"Listen! you hear the grating roar
Of pebbles..."See in text(Dover Beach)
With the imperative “Listen!,” Arnold directs readers’ (or perhaps his wife’s) focus to the sounds at Dover Beach. The adjective “grating”—a grinding, harsh quality of sound—and the noun “roar”—a full, deep, prolonged noise—create a vivid auditory image of the movement of the pebbles as the waves push and pull them along the shore.
"the moon-blanch'd land..."See in text(Dover Beach)
Arnold’s description of the shore evokes strong visual imagery of the white coastline. The moon is a source of pale, white light, which “blanches,” meaning “whitens,” the land. Also, the notion that the moon can whiten Dover Beach creates a sense of beauty and wonder at the power of nature.