This is technically more than one line, but it is one thought broken up by grammar:
“You have mistaken cruelty for strength, Darion. A true leader tempers his strength with compassion and humility, two traits that you lack, and look at where it has gotten you”, Daecon said with a snarl. “Now, I am giving you a final warning, do not test the limits of my compassion. I will not kill you, but I can certainly hurt you. You’re already treading on very thin ice.
I also like this one. It's actually in the same chapter and only a few paragraphs after the quote above:
“I will not personally kill you, Darion, nor would I have any other person be responsible for your death. Killing you would only create another murderer, and causing you to suffer one only death would not be sufficient punishment for your many acts of murder"
I feel these lines show that Daecon has truly "Found his way" and is rising to his new position as king rather nicely.