What picture of life and human condition is being painted in the poem?

Arnold's "Dover Beach" paints a picture of the human condition in England at a specific moment in time, when the "eternal note of sadness" is being pulled in by the waves, the "bright girdle" of faith having ebbed away. The poem reflects Victorian anxieties about the so-called Crisis of Faith, or the change in religious attitudes driven by scientific advancement. The human condition, as described in this poem, is a "melancholy" one where confusion is allowed to reign: at this moment, the people are "as on a darkling plain / Swept with confused alarms of struggle and flight."
However, this melancholy uncertainty born of confusion is not new to these particular "ignorant armies." Rather, the poet says, the "eternal note of sadness" was equally heard by Sophocles, who also considered the "ebb and flow / of human misery." Where there is uncertainty, and where faith is "retreating," humans are left in a world which "hath really neither joy, nor love, nor light," however beautiful it may seem. The only suggestion the poet can make is that we "be true to one another," as this at least would give one element of certainty amidst the "confusion."