What did Lincoln mean by 'the last full measure of devotion'?

".... 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. ......"

Gettysburg Address

by

Abraham Lincoln, President of the USA

November 1863