Grace was vital in forming the grown up March who decides to enlist and fight in the Civil War against slavery. It is the account that he gives ofhis time at the Clement's plantation, and of the whipping that Grace receives on his behalf, that clearly shows him the evil in slavery and the injustice of black-white relations. Note how this is reflected in the following quote, which comes as the young eighteen year-old March exchanges eye contact with Grace after her whipping has finished:
If an anvil had fallen from the sky at that moment and landed upon me, I could not have felt more crushed.
This sense of guilt and responsibility is something that haunts March for the rest of the novel, even after Grace, at the very end of the story, has released him from any obligation he may feel he has towards her.
In the same way, his relationship with Marmee helps to develop March's character in the way that he feels that he always has to work hard to live up to the standards that Marmee has and her fierce, anti-slavery beliefs. It is this in part that leads him to enlist in the Civil War and fight against the forces that champion slavery, as he seeks to make himself worthy for his wife. His account of her beliefs about slavery and her struggles against it lead him t become involved in transporting slaves illictly through to Canada and freedom. Both Marmee and Grace therefore have a massive influence on March's character and this can be seen in the man that records his thoughts and feelings in this novel.