Beginningless #4: The beginningless self-nature has been awakened.

Koan:

Seikenko of Cho composed a gatha as he was enlightened upon hearing thunder strike.
Sitting in the room in absolute silence.
Mind-source unmoved, filled like still water.
The striking of thunder has opened the gate of the head’s crown.
The beginningless self-nature has been awakened.
Present the implication or content of each line.

Knock, knock, who's there? Maybe this awakening is just like unexposed film—full of potential and ready for action.