The theme is one man may sacrifice for the many lives of others.
" Excellency, a man is flying.
The emperor Yuan did not move.Instead he looked at the great wall of china now taking shape out of the furthest mist in the green hills, that splendid snake of stones across the entire land.
who is to say that someday just such a man, just such an apparatus of paper and reed might not fly over and drop huge stones upon the Great Wall of China.
"Oh,said the emperor, closing his eyes, look at the birds, look at the birds."
These quotes led up to the theme by showing the reader that the man who made the flying was killed so that no body else could make them and fly over the great wall of china and drop huge rocks on the wall.