Question

what was lincolns intention behind writing and delivering \the gettysburg address\?
reasons why my parents should let me stay up late and watch scary movies
to persuade the people of the union that they should not give up or despair over the losses of war
to entertain the people of gettysburg and lift their spirits

Explanation:

The Gettysburg Address was delivered after the bloody Battle of Gettysburg, at the dedication of a soldiers' cemetery. Lincoln's goal was to reframe the war as a fight to uphold the founding ideals of the U.S. and encourage the Union to persevere despite heavy losses, rather than entertaining the public. The first option is entirely unrelated.

Answer:

to persuade the people of the Union that they should not give up or despair over the losses of war