Matthew Arnold belongs to the Victorian Age where there is a conflict between science and Religion. And because of the publication of Darwin's "Origin of Species"(1859), there is happened to be more of faith upon religion made a big gap among the common fellow beings.

       Here Arnold uses the image of sea to establish his view point. He here makes a comparison between sea and faith. Here, 'faith' refers to religious faith which is in Arnold's time - Victorian Era lost rapidly, owing to the influences of materialism and science. He means that, in the past religious faith was full and all the people paid deep respect to their religious faith just as the English channel as seen by the poet was full. The world was then dominated by religion. But I'm Victorian time that religious faith was completely engulfed by the doubts and questioning.

            The image of sea of faith is apt here in describing the time when spiritual faith held a powerful sway over men's mind . Of course, the poet's reflection is pessimistic and I'm the sad degradation of human life. This is  a part of the criticism of life which he has looked upon as the basic function of poetry as he defines "poetry is at bottom a criticism of life."