Dramatic Irony: Why is John struck by Hale’s declaration that “some secret blasphemy” has caused all of the confusion? Dramatic irony occurs when readers know more about a situation than a character does.
Hale's words are a coded message to John Proctor that comment upon Procyor's adultery. When he refers to "Some secret blasphemy that stinks to Heaven? Think on cause, man, and let you help me to discover it. For there's your way, believe it, there is your only way..." he is saying Proctor needs to confess his sins and humiliate himself in order to escape being charged with witchcraft. Proctor is already in conflict with the village's authority figures because he has publicly complained about their corruption. Despite Proctor being one of the only townspeople who sees throguh the sham of justice inherent in the witch trials, his own guilt surrounding his sexual liaison with Abigail prevents him from feeling like he can truly condemn anyone else.
The dramatic irony of the situation is that John and the audience know that he has committed adultery. Hale does not know that fact, yet he contemplates that some dark sin must be the cause of Salem's troubles. The full quote gives better context.
Man, we must look to cause proportionate. Were there murder done, perhaps, and never brought to light? Abomination? Some secret blasphemy that stinks to Heaven? Think on cause, man, and let you help me to discover it. For there's your way, believe it, there is your only way, when such confusion strikes upon the world.
Hale says that for Salem to be in such trouble now that there had to be some kind of major and proportional cause. Big punishment for Salem means some major sin happened. He doesn't know what that sin might be, which is why he hypothesizes a possible murder cover up. Hale is saying that when the cause is brought to light, the hysteria gripping Salem will begin to diminish.
The comment deeply affects John, because he believes that he is the secret sin. He believes that his adulterous affair with Abigail is at the root of the witchcraft hysteria. He might be correct too. Miller writes a strong case that Abigail is doing everything in order to get Elizabeth Proctor out of John's life. John is in a tough spot. He knows that he has the power and ability to discredit Abigail, but it will be at the cost of his own reputation.