Registration under GST (Sec 25)

1. What is the exact difference between sec 25(4) and 25(5) because both these subsections talk about registration in more than one state/UT.
2. If a person voluntarily obtains registration in one state (State 1)and is not required / does not voluntarily obtain registration in another state(State 2). Is the person required to obtain registration in the other state (State 2) u/s 25(5)?
Thank you.