In "Dover Beach," a dramatic monologue, the speaker describes a peaceful seascape in the first fourteen lines. The only thing interrupting the serenity is the sound of the pebbles being flung around by the waves:
Listen! you hear the grating roar
Of pebbles which the waves draw back, and fling,
At their return, up the high strand, (9-11)
This sound marks an "eternal note of sadness" upon the scene. The speaker then suggests that Sophocles considered the grate of the waves on the pebbles as representing human suffering which he (the speaker) contemplates now (as he narrates the poem). The Sea of Faith, perhaps spiritual assurance of his individual and greater social world, has receded and therefore he is seeking some greater meaning of life to replace the loss of faith. (Arnold believed that Christianity was dead and supposed what culturally unifying theology or ideology might replace that.)
Considering the empty void of a world the speaker sees while contemplating these natural metaphors, he turns to his lover thinking they can find meaning and stability of purpose in each other. One of the themes here is the individual's search for a sense of purpose and meaning in life. The speaker is confused by the dichotomy of the world as potentially serene and potentially like a battlefield. Thus, meaning in life might not be found in nature or in culture ("Where ignorant armies clash by night.") Instead, meaning could be found between two people. Love is certainly a theme here but it is the tool used to suggest the larger theme which is a search for meaning when spiritual or philosophical doctrines are no longer applicable.