Was the phrase first used by Abraham Lincoln to convey to men of the Union to give their lives to serve their country and to win the Civil War? Does it mean to give all you have and by all means necessary? Comments are welcome.
Here is the complete sentence: It is rather for us to be here dedicated to the great task remaining before us -- that from these honored dead we take increased devotion to that cause for which they gave the last full measure of devotion -- that we here highly resolve that these dead shall not have died in vain -- that this nation, under God, shall have a new birth of freedom -- and that government of the people, by the people, for the people, shall not perish from the earth.
He wasn't necessarily asking men to give their lives, but to continue fighting with increased devotion and not to give up the struggle because of the men who had already given their lives. The fact that men had already died to reunite the states was a reason to continue the fight with increased devotion--so that their deaths would not be useless, and so the United States would not cease to exist.