Dover Beach-Matthew Arnold

Poster¡G Claire at 17:4:34 1/2/98 from
Dover Beach -- Matthew Arnold 

Background: The poem is written in the year of 1851, when after the revolution in 1848, the countries in Europe are cruelly oppressed. The wars are constantly happened. 
Content: The first stanza (line1~5) shows the harmonious atmosphere, the poet used the words such as- calm, fair, tranquil to indicate peace. " Gleams and is Gone ". 
Does " gone " imply that the peace will no longer exist? From line 1~5, it set the background, in line 6, " only " is a turning point, the feeling begins to change after the word "only". The sound of the pebbles, drawing back and flinging, " begin and cease, and than begin". It repeats the action of tide, in addition, the pebbles are in a helpless position, and they're moved, dragged by the wave despite their own will. 
"Grating roar" sounds like the marching of armies. Why the cadence tremulous? Slow? And then bring the sense of eternal sadness? It's the poet's feeling by seeing the sight, hearing the tide, all these bring sadness to the poet. 
The second stanza leads us back to ancient time, in memory of the tragic poet Sophocles in Greece, Sophocles once was arouse the feeling of sadness by listening the wave on the Aegean, although time and space has been changed, we still feel the same. "Turbid"ebb and flow is much like the turbid world, it follows "Of human misery" what misery does human have is the saddest one? War, may be? 
In the third stanza, "The sea of faith" can be Christianity or some belief or ideal which human possess, however, it declined. The poet used the word "Melancholy, long, withdrawing, retreating" to show his own disappointment. "Was" and those words " full" "round" contrast with "Now" "Melancholy, withdrawing". Line 21 and 22 show the "Faith" "was" prosperous, "naked shingles" leave the feeling of pity, decline, and sorrow. 
The last stanza, why the speaker said "Let us be true?" Since the world seems in disguise, it looks so various, beautiful, new like a land of dreams, but actually rarely joy, no love, light, certitude, peace and no help for pain. "Darkling plain", I think here it may be implied that war is like a dark cloud cover where we are. "Confused alarm" "struggle" also shows the sight of war. In the last line, the poet blamed the armies ignorant for they spoil the peace destroys the happy land.