On march 19, 1965 in selma, alabama, a group of civil rights activists formed outside of city hall. the heartbeat of the group grew stronger as more supporters joined, which pumped more life into the peaceful protest. how does the personification of the activists affect the writer's message?

Personification has to with giving human attributes to non-human objects. In this case, there is no such thing as a "physical heartbeat of the group."  A group cannot have a heartbeat. However, figures of speech (personification is one of them) are helpful in order to effectively convey a message.

Personification helps send the reader a message that the activist group acts as one body. It lets the audience know that the activist group is united, acts as a solid community, and as one united front. Therefore, using personification creates a stronger tone that effectively conveys a message.