The lines "Take up our quarrel with the foe: / To you from failing hands we throw The torch;" supports the theme - the living carry on what the dead cannot. The torch signifies the living continuity of the cause they are fighting for. These lines give a challenge to the ones who are still living to not stop but keep going.
Explanation:
intend to convey or refer to (a particular thing); signify.
"I don't know what you mean"
