Lincoln uses parallelism in this excerpt to

acknowledge the limitations of the memorial ceremony.

criticize the audience for its disinterest in the war.

encourage soldiers to continue the fight for national unity.

emphasize the need for improved military strategy.

Lincoln uses parallelism in this excerpt to acknowledge the limitations of the memorial ceremony. In this excerpt, it is parallelism because he instilled the words side by side such as dedicate and consecrate, living and dead, add or detract to clearly emphasize that what the men did will forever remain as time will pass by.