It's after Margaret commits infanticide and the community condemns this poor 15 year old girl for it, and sentences her to death. Here she is, in the dungeon where Faust breaks in and tries to break her from her shackles. However, the prison is in her head, that she cannot escape. Faust says take one step out of here but she can't take that step outside of her guilt and shame. That's what ultimately kills her.

Faust's words: Let the past be past.

These words coming from one of thee greatest writers ever, western civilization's last polymath, meant a lot to me.