As we all know, Odin enchanted Mjolnir in Thor:
whosoever holds this hammer, if he be worthy, shall possess the power of Thor.
At this stage, I interpreted it as one can lift the hammer and control lightning if they are worthy. But then in Thor: Ragnarok:
Odin: The hammer was to help you to control your power, to focus it. It never was your source of strength.
So Mjolnir is not part of the "power of Thor". Thor can control lightning even without the hammer, it just helps him control the lightning better. My question is, why does someone need to be worthy to wield Mjolnir? It is not the power of Thor from this perspective.