Lincoln's purpose is to unite the Nation. Even though the Civil War was close to it's end, with the Union side clearly overpowering the south, it wasn't all so certain yet, this was Lincoln second and last term, ending the war as soon as possible was the first priority of his administration. The president noticed that both North and South pray, they both read the same bible and they both believe in the same God, therefore he used a biblical quote in his speech, so both sides could note it.
