When the Jedi Council senses the rise of the dark side about a century or two before the end of the Republic, Yoda suggested that it heralds the imminent coming of the Chosen One, prophesied to bring balance to the Force. Anakin Skywalker is confirmed to be indeed the Chosen One, but what exactly is his intended destiny?
Foremost is the Jedi belief that he will end the Sith Order once and for all. Even though he, as Vader, eventually sacrificed himself to kill Palpatine, thus ending both the master and the apprentice, the Sith Order was not truly ended. Palpatine eventually returned before dying for good, and the Sith Order under Krayt's Rule of One yet lives. Not to mention that the greatest champions of the dark side have always come from the light. If Anakin was chosen to end anything, he was extremely sloppy.
But what about the other possibility? The Father decreed that the Chosen One is meant to replace him in keeping the Son and the Daughter in balance. By choosing to leave, he had supposedly failed his destiny, allowing the Force to tilt in severe imbalance, and this consequence is supposedly revealed and only then corrected in some measure a great many years later by his son Luke.
In any case, Anakin seems like a massive failure in life. But what was his true purpose?