The slide to unlock gesture is not possible to enable in iOS 10. It is gone. It is possible that a future iOS version will allow the Slide-to-Unlock gesture to return, but for now it appears to be removed permanently. Many iOS users miss the Slide-to-Unlock gesture so they will probably bring it back soon. I wouldn't recommend it as it is unreliable and risky, but it is possible to down-grade to iOS 9 and bring back the old look together with Slide-to-Unlock gesture.