In some respects, process of elimination might be the best element to be used here.  The Gettysburg Address was written in 1863, at the near midpoint of the Civil War. Lincoln was elected in the election of 1860 and his inaugural address took place in 1861, which predates the quote.  This puts us at a one out of two situation between the Emancipation Proclamation and the State of the Union Address for that year.  Frankly, without more information in terms of specific dates, we might be at a loss.  On one hand, the document in question could be a State of the Union Address.  Yet, I think one would have to consider the context of Lincoln's words.  The fact that he would overtly state that he does not require the counsel of his cabinet, and that he is merely informing them of his actions and it is not up for debate and discussion would indicate that what he convened them for is important and the document is extremely relevant.  Certainly, State of the Union Addresses like this are important, but it seems to me that there is a gravity here that goes beyond a yearly address.  The Emancipation Proclamation was issued on September 22, 1862.  Consider Lincoln's words after signing it:

I never, in my life, felt more certain that I was doing right, than I do in signing this paper.

Given this and his demand for his cabinet to listen and not offer counter advice, it seems to me that it is the Emancipation Proclamation that is the document in question.