to sit light and erect

[beachboy]

The clear-eyed girl, sitting light and erect on the couch.
What does to sit light and erect mean?

 

[emsr2d2]

The clear-eyed girl, sitting light and erect on the couch.
What does to sit light and erect mean?

Sitting "light" means she was just gently seated on the sofa, perhaps towards the front edge. She wasn't fully squashed up on it, looking very comfortable and snug.

Sitting "erect" means she was sitting very upright, her spine was very straight.

 

[Amigos4]

The clear-eyed girl, sitting light and erect on the couch.
What does to sit light and erect mean?

Beachboy, imagine yourself sitting on a couch while watching a soccer game on TV. I bet you would not be 'sitting light and erect'. You would be comfortably sprawled-out while snacking on your favorite food and beverage! You probably would not want to invite the 'clear-eyed girl sitting light and erect' to watch the game with you!