KING HENRY IV "The time will come, that foul sin, gathering head, Shall break into corruption:" so went on, Foretelling this same time's condition And the division of our amity. (3.1.5)
Here, King Henry recalls King Richard II's prophesy. (Remember, King Richard II is the guy King Henry IV bumped off the throne back in the first play of the tetralogy, Richard II.) We're interested in the language that Henry quotes here. According to him, Richard foresaw that Henry's "sin" (deposing a king) would gather to a "head" and then "break into corruption." In other words, Richard predicted that Henry's sin would lead to civil rebellion. At the same time, the description makes the rebellion sound a lot like the way puss comes to a "head" and then oozes from a sore. So, even though King Henry has previously said that the commonwealth's diseased body is all the rebels' fault, this passage suggests that Henry may feel as though he is the cause of the country's "illness." After all, he's the one who sinned. Compare this passage to 3.1.4 above.