Eisenheim's explanation to Inspector Uhl why he would summon the spirit of the Duchess von Teschen every performance, even when it might get him arrested. He simply says: "To be with her."
Inspector Uhl's speech just before that, essentially pleading with Eisenheim, a man he respects and admires, not to evoke the wrath of the Crown Prince any further.
Inspector Uhl: Herr Eisenheim, I don't want to arrest you. I'm a cynical man, God knows, but if your manifestations are somehow real, then even I'm willing to admit you're a very special person; and if it's a trick, then it's equally impressive - either way, you have a gift. So don't make me put you in jail!
The very end, when Eisenheim is reunited with Sophie at their farm and they are implied to live happily ever after.