The speaker's state of mind in this poem is described as "fervourless," or lacking in any kind of enthusiasm for the world around him. He sees the wintry world around him as reflective of this state of mind: it seems to him "shrunken," and Hardy makes an allusion to the anxiety that struck at the turn of the twentieth century when he refers to seeing "the Century's corpse" in the lay of the land. He is clearly feeling uneasy, unsure of himself and the world around him, and is seeking some hope when all he can hear is a "death-lament."
The voice of the thrush, then, goes some way towards providing this for him. Its "joy illimited" is very different to what the speaker is feeling. Indeed, he notes that there is "little cause for carolings" in the world he sees; he cannot understand what the bird is experiencing that he is not. And yet, the song of this thrush does give the speaker "some blessed Hope." While he himself is still "unaware" of what that hope might be, the song of the bird seems to spread some happiness into the desolate landscape and gives the speaker a shred of hope to cling to: he may not be able to see the cause of the thrush's happiness, but he does believe that it is there somewhere in the world.