What are some examples of literary devices in Abraham Lincoln's Gettysburg Address?

Abraham Lincoln was one of the great orators in the history of American politics. When writing the Gettysburg Address, Lincoln utilized a number of literary devices to draw the attention of his audiences.  Hopefully, this will get you moving in the right direction:

"Fourscore and seven years ago our fathers brought forth on this continent a new nation, conceived in liberty and dedicated to the proposition that all men are created equal."

The opening statement is an example of the use of allusion.  Allusions are references to things from the past, whether they be famous people, literary works, or events.  In this case, it is a reference to the Declaration of Independence and the Revolution.  The phrase ".and that government of the people, by the people, for the people" could also be an allusion to the United States Constitutions which states "We the People."  That statement is also an example of repetition.  

 "We are met on a great battlefield of that war."

Imagery is used to illicit mental pictures from the audience and often appeals to the senses.  This short sentence is very powerful in that it conjures up images of bravery and valor in battle.  It would have an even more dramatic response as it was being delivered on a battlefield where many soldiers perished.

"we cannot dedicate—we cannot consecrate—we cannot hallow."

Anaphora is the deliberate use of repetition in order to make speech or text more interesting or artistic. This was an interesting transition to the part of the speech that speaks of the ultimate sacrifice paid to protect liberty.

"The world will little note nor long remember what we say here, but it can never forget what they did here."

This is an example of antithesis, in which two opposing ideas are joined to achieve a contrasting effect.  Lincoln uses this sentence to describe how insignificant he is to history when compared to the soldiers that died in the Civil War.  

"that this nation under God shall have a new birth of freedom"

This is an example of allegory in that it compares an abstract idea like "freedom," to the more concrete notion of being born.  In this case, he discusses the rebirth of the United States should the Union win the United States.