In this bleak but poignant poem Arnold describes the context of his times, where he felt that faith was retreating like the retreating tide from his society, leaving people naked and exposed to the world and its harshness and cruelty. In Arnold's vision of the world, the only form of faith that remains is that which is based on love and the relationships that we have with our loved ones. Note how he develops this theme in the last stanza:
Ah, love, let us be true
To one another! for the world, which seems
To lie before us like a land of dreams,
So various, so beautiful, so new,
Hath really neither joy, nor love, nor light,
Nor certitude, nor peace, nor help for pain;
And we are here as on a darkling plain
Swept with confused alarms of struggle and flight,
Where ignorant armies clash by night.
Note how the bleak image of Arnold's world is developed. It has no 'joy, nor love, nor light / Nor certitude, nor peace, nor help for pain.' Existence is described as being on a 'darkling plain' where 'ignorant armies clash by night.' The only recourse or faith that is available therefore is expressed in the speaker's plea to his love for them to be true to each other. Without religious faith, faith in our relationships and with our loved ones is the only security we can have in such a world.