What did Lincoln mean by with malice toward none?

That phrase comes from the closing of my Second Inaugural Address, delivered in March of 1865, and I think it bears reading in its full context rather than in isolation. As I said there, “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” What did I mean by it? Simply this: that when the war ended, the South was not to be treated as a conquered foreign enemy to be humiliated and plundered, but as estranged countrymen to be welcomed back. Four years of terrible war can breed a thirst for punishment. I wanted to check that impulse before it poisoned the peace. But notice that malice toward none is paired immediately with firmness in the right. I did not mean a weak or indifferent forgiveness that calls wrong things right. The offense of slavery I had called out plainly in that same address — “It may seem strange that any men should dare to ask a just God's assistance in wringing their bread from the sweat of other men's faces” Justice had to be done. What was to be set aside was spite — the desire to make men suffer beyond what justice requires. Charity and firmness together. That was the whole thought.