What was Lincolns second inaugural address about?

Put simply, the address related three ideas:

1. The war was not a controlled action by either side; it had its own identity, independent of the people of the North or South;

2. Slavery was a truly national sin, the responsibility of both North and South. For that reason, the penalty for this sin must be paid by the entire nation (..."and that he (God) gives to both North and South, this terrible war, as the woe due to those by whom the offense came...");

3. Despite the fact that "both read the same Bible, and pray to the same God", neither party could claim God's special favor; God's justice would be meted out in His own time, not man's, and it is simply our responsibility to behave as a penitent people, striving "to bind up the nation's wounds" and to achieve "a just and a lasting peace, among ourselves, and with all nations."