What are the differences between destiny and purpose?

The purpose of something is the reason it is created. Its destiny is where it is going to end up in the end. These are not necessarily the same thing. The purpose of a hammer is to whack in nails. But the destiny of a particular hammer might be to be abandoned, go rusty and be thrown in the dump. Or it might be to be used as a murder weapon and end up as evidence. Or, it is just possible that it might be used to whack in nails a lot.