Joe burns Pip's indenture in the fire, implying that he cares more for Pip's future and happiness than money.
Explanation:
The reason why Joe burns Pip's indenture is that he is giving Pip the chance to become a gentleman since Mr. Jaggers, has told Pip and Joe that a mysterious benefactor offers a great deal of money, but he has to follow a set of rules, being the most important one to never ask who this mysterious benefactor is.
By burning Pip's indenture in the fire, Pip is now "free." He can become a gentleman instead of being just a blacksmith. This is symbolic of Pip getting a fresh start, a new beginning.
