Hello there!
One of Lincoln's opinions is that USA is a nation founded on the idea that all men are created equal and that there is no difference. Even though this is in the Declaration of Independence, it can be argued that this is not true since America still has slavery.
In addition, he believes that the government by the people will continue on. This statement, at the time, is supported by the fact that the Union is doing everything they can to preserve and keep the nation. :)
Finally, another opinion by Lincoln in this speech is that the world will not remember what is said at Gettysburg. Nowadays, this is not true, because it is one of the most studied speeches in the history of America.
Hope this helps!