Armand, as stated in the previous post, does treat his slaves badly. It is after his marriage to Desiree and the birth of their child that Armand begins to treat his slaves well. The passage which depicts Armand's change is
"Oh, Armand is the proudest father in the parish, I believe, chiefly because it is a boy, to bear his name; though he says not - that he would have loved a girl as well. But I know it isn't true. I know he says that to please me. And mamma," she added, drawing Madame Valmonde's head down to her, and speaking in a whisper, "he hasn't punished one of them - not one of them - since baby is born. Even Negrillon, who pretended to have burnt his leg that he might rest from work - he only laughed, and said Negrillon was a great scamp. Oh, mamma, I'm so happy; it frightens me."
Even, as noted by the quote, Desiree notices how Armand has begun treating the slaves. Desiree attributes this to their child.
Initially, before marrying Desiree, Armand is extremely harsh and cruel in his treatment of his slaves. He seems, however, to have had an affair with one of his lighter-skinned slaves, so that he is thus a hypocrite in his treatment of his slaves. After he marries Desiree, he treats his slaves better than he had been treating them -- a fact suggesting that his treatment of them is not objective or reasonable in any way but is merely a matter of emotional an personal whim. His treatment of his slaves is a good example of how one person should not treat any other person. Ironically, given his racial background, Armand himself could easily have been a slave and might have learned from personal experience how it feels to be treated as one.
While Armand is married happily to Desiree and enjoying the expectation of their coming baby and the final ecstasy of the infant's presence, he treats his slaves with kind good humor, even turning a blind eye when one slave feigns injury so as to gain rest from his labors:
"Even Negrillon, who pretended to have burnt his leg that he might rest from work - he only laughed, and said Negrillon was a great scamp."
The other editors above make a number of valuable comments. What we can learn from Armand's change of treatment of his slaves is that we often project our own moods onto those around us. During a time of slavery, this can mean that slaves receive the brunt of their master's emotions. It is true for us today though. If I, as a teacher, have a bad day, I have much less patience with my classes than I would do normally.
Armand's treatment of slaves turns out to have its motivation in his own heritage. It could be argued from a psychological standpoint that he is cruel to the slaves when he hated that potential part of himself, but when the baby is born, he thinks it is proof that he is white, and therefore doesn't have that external projection. When the baby comes to have darker skin, his worst fears are confirmed.
And what lessons might we learn from that?