Apple makes a dramatic change to how you unlock your iPhone in iOS 10. There is no longer an option to “Slide to unlock”. Instead you have to press the Home button. Then Touch ID will be used to unlock the phone. If Touch ID is not enabled or failed to unlock, you get the option to enter the passcode.
Previously, those with Touch ID enabled can simply rest their finger on the home button, without pressing, to unlock. If you’re fed up with this additional press-home-button-to-unlock, you can switch back to the way it used to work in iOS 9.
Go to Settings app > General > Accessibility > Home Button. Turn on the “Rest Finger to Open” switch. That’s it.