Then I reversed the spell, showing you my goodness As well as my power. I saw
Suddenly, our focus switches from Odysseus' men to Odysseus himself.
Circe continues to tell the story of her first encounter with these men, reminding her sweetheart of the fact that she eventually released them from the spell that made them into pigs.
She's making a point of reminding Odysseus of how powerful she is and of how nice she can be.
We see the sorceress in her asserting her power to a visitor, and we see the lover in her demonstrating her humanness to a man she's trying to impress. She speaks to Odysseus as though she were both a queen and his honeypie. Talk about mixed signals.
Line 11 is especially long and is made longer by that present participle (read: a verb that ends in an –ing), "showing." This line seems much more conversational than the clipped sound of the three previous lines. Why do you think this is?
Line 11 mentions Circe's goodness, and line 12 mentions her power. In this way, these two lines become like two different faces of a coin. Circe seems to want to drive home the fact that she's both powerful and good, and that we'll have to "heads or tails" it to find out which of those characteristics she is at any given moment.
At the end of line 12, she simply says, "I saw." Through the use of enjambment (line break) we are left hanging.
What did Circe see? We know that she's a sorceress, so the potential for seeing things in the future, in the past, in dreams, etc. is huge. By isolating "I saw" at the end of this line, we are reminded of the fact that Circe is magical enough to do things like predict the future.