Understanding Character Through Stage Directions

Consider the following excerpt from a play, which includes stage directions:

As the curtain rises, we see a cluttered room filled with old books and scattered papers. A single dim light bulb hangs overhead, casting a shadow that flickers like a heartbeat. In the center of the room, a chair stands empty. SARAH walks in, hesitates at the threshold, and glances back towards the door before stepping further inside.

Stage Directions: SARAH pauses, her expression a mixture of anxiety and determination.

How do the stage directions enhance our understanding of SARAH’s character at this moment?