Translation:

111. There is in their stories instruction for men endued with understanding. It is not a tale invented but a confirmation of what went before it a detailed exposition of all things and a Guide and a Mercy to any such as believe.

Notes (Tafseer)

1796. Their stories, i.e., the stories of Prophets or of the wicked; for the two threads inter-twine, as in Joseph's story.

1797. A story like that of Joseph is not a purely imaginary fable. The People of the Book have it in their sacred literature. It is confirmed here in its main outline, but here there is a detailed spiritual exposition that will be found nowhere in earlier literature. The exposition covers all sides of human life. If properly understood it gives valuable lessons to guide our conduct,-an instance of Allah's grace and mercy to people who will go to Him in faith and put their affairs in His hands.