I think that Brooks' work shows the need to stand up for one's beliefs in a couple of ways. The first would be through March, himself. He refuses to remain silent when he recognizes that there are some basic elements for which compromise is inappropriate. One such reality is the way in which people of color are treated. The fact that March violates social edict in educating Grade and seeking to emancipate and help those who are enslaved is a part of this. Additionally, March speaks out against soldiers who are abusing their power. March's entire state of being is done to ensure that his beliefs are not compromised and silenced. In this, March represents a reason why the Civil War was inevitable. The lack of silencing one's convictions leads to unavoidable conflict, something that March understands and yet from which he does not shy.
Marmee also represents this idea of needing to stand up for one's beliefs. She recognises her husband's fundamental hypocrisy in how he can preach liberation for everyone else, yet he does not recognize how he is stifling his wife. Marmee does not stand silent for this, as she speaks out to March as to his hypocrisy. In this, she represents how people must speak out for their beliefs, regardless of condition and of social context.