Hello. You did not say which poem this question refers to, which makes it impossible for me to give you an exact answer. However, I will try to help you by showing you what the tone of a poem is and how those words can change it. I hope it helped you.
The tone of a poem is the feeling that the poem gives to the reader while reading. A poem with melancholy and painful words has a sad tone, a poem that presents nature as something inspiring, has a reflective tone, for example.
The words shown by you, in the question above, refer to something difficult to be perceived and visualized, requiring a certain effort. With that we can project that these words modify the tone of the poem presenting a tone of search, of difficulty and effort.
