Answer: to emphasize the intense responses of audience members to Antony's speech
Step-by-step explanation:
When Mark Anthony gave a eulogy for Julius Caesar who had been assassinated by several members of the Roman Senate, he did so with such emotionally charged rhetoric that the audience were so riled up that they wanted to kill his assassinators to avenge the great man painted by Mark Anthony.
The camera therefore focuses on the faces of the individual members of the audience who had been riled up, to show just how intense their response to this speech that riled them up was.