Answer:
The answer to the question: What does Lincoln mean when he says that soldiers gave "the last full measure of devotion", would be: that these soldiers gave everything they had, including their lives, for the sake of what was good, which was keeping the Union together.
Explanation:
The words mentioned in this question were part of a speech that was given by U.S President Abraham Lincoln on November 19, 1863, at the Soldier´s National Cemetery in Pennsylvania. The speech is historically known as the Gettysburg Address. This address came at one of America´s most difficult times, when the country has divided into North and South and everything seemed like it would come apart. At this point, Lincoln delivers this speech, the best known of him, to let people know that America will remain as one and that those brave soldiers who lost their lives did so for the greatest good. In those words of the speech, Lincoln is giving these soldiers the highest honor possible; he basically named them the bravest of the brave.