Lincoln's Second Inaugural

Garry Wills, who wrote Lincoln at Gettysburg, the most definitive exegesis of the address, also published an article in The Atlantic on the Second Inaugural, titled "Lincoln's Greatest Speech?"
Wills notes that he is not alone in thinking the Second Inaugural may be Lincoln's best, noting that Lincoln himself was pleased with his effort:

Eleven days after delivering it he wrote to Thurlow Weed, the Republican organizer in New York, that he expected it to "wear as well as -- perhaps better than -- any thing I have produced."

Wills notes the speech's brevity:

The first thing to admire, then, is the discipline that kept him from saying anything more than what he considered essential, just as at Gettysburg.

One feature of the speech is the repeated comparison of the two sides in the Civil War. Lincoln neatly contrasted the willingness to go to war with the unwillingness to let the Union die:

Both parties deprecated war; but one of them would make war rather than let the nation survive; and the other would accept war rather than let it perish. And the war came.

He compared the two sides in their devotion to God:

Both read the same Bible, and pray to the same God; and each invokes His aid against the other.
...
The prayers of both could not be answered; that of neither has been answered fully.

Wills notes that Lincoln did not declare the triumph of righteousness, but instead invoked God's judgment:

Fondly do we hope -- fervently do we pray -- that this mighty scourge of war may speedily pass away. Yet, if God wills that it continue, until all the wealth piled by the bond-man's two hundred and fifty years of unrequited toil shall be sunk, and until every drop of blood drawn with the lash, shall be paid by another drawn with the sword, as was said three thousand years ago, so still it must be said "the judgments of the Lord, are true and righteous altogether."

Wills notes that the speech contrasts judgment and mercy:

But the appeal to "Gospel forgiveness" is preceded by a submission to "Torah judgment" and divine wrath -- an odd vehicle for a message of forgiveness.

While leaving judgment to God, and with the end of the war in sight, Lincoln delivered his famous peroration:

With malice toward none; with charity for all; with firmness in the right, as God gives us to see the right, let us strive on to finish the work we are in; to bind up the nation's wounds; to care for him who shall have borne the battle, and for his widow, and his orphan -- to do all which may achieve and cherish a just, and a lasting peace, among ourselves, and with all nations.