Jimmy McGill will become the completely immoral Saul Goodman before Better Call Saul ends, but that doesn't mean that his older brother Chuck McGill always has the moral high ground. In the Season 3 premiere, Chuck reveals he taped Jimmy confessing to changing the Mesa Verde files to Howard Hamlin. While Howard doesn't understand what Chuck is trying to accomplish by recording his brother, Chuck wants to ruin Jimmy on Better Call Saul and appears to have a master plan to do it.
During the April 10 episode, Howard points out that the tape of Jimmy saying he tampered with Chuck's Mesa Verde files would most likely not stand up in the court of law or court of public opinion and says, "I can't think of a single use for it." Chuck, in his dimly lit home, responds with gleeful menace: "I can." Though exactly what Chuck is up to isn't obvious just yet, there is one thing that's crystal clear: he's using his electromagnetic hypersensitivity illness to his advantage just like he did in Season 2.
When HHM employee Ernie stops by Chuck's home for a supply delivery of ice, apples, and batteries, Ernie assists Chuck in changing out the batteries of his tape recorder and hears the recording of Jimmy's confession. If you think the timing of the tape is too convenient, your instinct is right on. Chuck's flipping of his wooden tongs and satisfied smirk at the end of the scene indicate that he had wanted Ernie to hear the recording all along.
Knowing that Ernesto is Jimmy's friend, Chuck masterfully manipulates the situation to have him think that he accidentally heard Jimmy's confession. From his fake outrage to his extreme warnings that Ernie shouldn't tell anyone what he heard, it appears that Chuck is banking on the fact that Ernie will tell Jimmy. Yet again, the why of Chuck's actions isn't explicitly revealed, but knowing the deep-seated animosity he has toward Jimmy, he's most likely hoping this tape will be the ruin of his younger brother's legal career. So, you can assume the cool and calculated Chuck thinks that if Ernie tells Jimmy what he heard, his more hotheaded brother will act out in a way that helps Chuck destroy him.
While Chuck is so certain in his moral righteousness, the more he becomes intent on destroying his brother, the more he reveals that his type of ethical ambiguity is perhaps even worse than Jimmy's. At least in Better Call Saul, Jimmy's intentions are typically to help someone out, even though his means might not be squeaky clean. But as outstanding of a citizen as Chuck thinks he is, he is using his powers of manipulation for pure evil. And his actions might just drive Jimmy to become Saul.