Question

how does the cuckoo's voice charm the poet

Answer 1

 The poet hears the cuckoo and is in awe and wonder on the off chance that it is something more than a winged animal. His marvel ascends from the memory of his youth when the cuckoo opens up the universe of creative energy to him. The cuckoo bird is an arranged image of innocence, gaiety, purity and boyhood.
Thus this is how the cuckoos voice charm the poet .