I left out the following sentences. Thank you for your suggestions.
1) The song of the birds and the reaper arouse pleasure and relief.
2) The language of the poem contains references to the language of sight (line 1) and hearing (line 7).
The language is quite simple but enriched by comparisons suggested by the poet's imagination.
3) The speaker says that the sound is more welcome than any chant of the nightingale to weary travelers in the desert, and that the cuckoo-bird in spring never sang (or has never sung)with a voice so thrilling. (or with such a thrilling voice)
1. This sounds as if both the birds and the reaper are singing. Is that what you meant?
2. I'd revise like this: ... references to the senses of sight and sound.
3. Is the "chant of the nightingale" sung to "weary travelers of the desert"?
Yes, "has never sung"
In both 1 and 3, you're dealing with dangling or misplaced modifiers. Take a look:
http://grammar.ccc.commnet.edu/grammar/modifiers.htm#misplaced