The two gentlemen appear in this scene to give a sense of the popular opinion of the events at the court. First, we find that they are very aware of all of the passing events, and they hold strong opinions. These are not Shakespeare's charming commoners, too distant from the court to comment on it; rather, these characters believe the king has made mistakes and is held too much under the influence of Wolsey. Showing the greater link between the nobles and the people in this play, the gentlemen are very interested in and moved by the fall of Buckingham.
Like many of Shakespeare's characters, Buckingham has learned much from his unfortunate fate. Buckingham delivers a dying man's oration, urging the crowd to learn what he has, that even when you are loyal to your friends, sometimes they turn against you without provocation. He now understands the truth and yet can forgive his accusers. Buckingham steers clear of accusing Wolsey of being the traitor or influencing the king, unlike his earlier railing against Wolsey. Perhaps he understands that his previous criticism of Wolsey led to his present circumstances; yet on the way to his death, he refuses to name names.
Buckingham will not go to the grave in anger, yet he does recognize the terrible irony of his fate. Like his father's death, Buckingham's downfall comes not through disloyalty but rather through too much loyalty to men who turned on them. The gentlemen suspect that Wolsey is behind Buckingham's downfall, but Buckingham's stance of forgiveness means that Wolsey gets away with it.
Buckingham is the first to be brought down and to make his speech of forgiveness; Katharine follows. It appears that Buckingham had to fall because he imagined he had a claim to the throne. Whether this claim was really in Buckingham's mind or merely an accusation by Wolsey is unclear. Either way the result is the same; none who even imagine a future without Henry's issue on the throne are doomed to fall. Again, this play is directed inexorably to the birth of Elizabeth, and no character in the way can live.