Lorax makes deals, he does not accept them from insignificant mortals.
A deal I shall make with you, however... take this pike, it is imbued with powerful Fel energies. When you find Goraluk Anvilcrack, slay him and drive this pike through his dying heart. His soul he bartered, his soul I shall have. Return the pike and return the breastplate that the thief stole and I shall teach you what it is that he was to learn.
Our pact you did not break. The soul I did take. The reward I shall make.