‘And the doors will be shut in the street, when the sound of the grinding is low, and one will rise up at the voice of a bird, and all the daughters of music will be laid low.'
This may refer to the fact that the doors will be shut because the aged man no longer goes out into the street. He also eats with difficulty with little use of the decayed teeth, so that there is little sound of grinding. Or the closed doors may be the man's lips as he grows weaker, seen along with the non-use of the teeth as eating and drinking becomes more difficult, or reference may be to the approach of deafness, the doors being closed so that he cannot hear sounds. Whichever way it is, it is emphasising his incapacity through old age.
Furthermore he cannot sleep through the night and rises with the birds, and yet is unable to hear the songbirds (the daughters of music) clearly so as to enjoy their music. Or the idea may be that when through the dimness he catches the song of the early bird he rises as he always has, only to remember that he cannot hear their songs properly, and that life no longer offers him anything but to endure until the end.