The power of a photograph to evoke a time and place. Maybe better put the power of the photographer to create a photograph through the medium of their camera and lens that evokes a time and place.
It is the art of the photographer to convey within that photograph some emotion or feeling that makes a connection with the viewers of their picture.
The power of photography - the photographer, the camera, the lens, the photograph - speaking to people - evoking the spirit of a time and place.