To expand on what Quartz mentions above, a jury is a final defense against a corrupt government.
In many small jurisdictions, the system consists of a group of individuals who work together every day and often socialize on a personal level - the judge goes fishing with the DA, the chief of police has regular lunches with a public defender, etc. They all get together for social events. It becomes a “boy’s club” of sorts. They work as a unit - scratch my back and I’ll scratch yours.
(Disclaimer: I don’t intend to say that all jurisdictions work as above, but it happens.)
One day you end up in a misunderstanding with a member of the “boy’s club”, or maybe with a friend or relative of a member. Bogus charges are filed, and you are railroaded through the system. The game is stacked against you, and you have no conceivable way to beat the charges and remain a free man… except for the existence of a jury.
In theory, a jury is incorruptable (unless you argue that a particular microcosm of society is corrupt, such as instances of racist juries in mid-20th-century southern U.S.) A jury of your peers has the power to see through an unjust prosecution and make a proper verdict. Without a jury, you are at the mercy of the system.
Obviously, the above is a completely made-up example, but the truth is that similar instances have occurred. Take the recent case of a Pennsylvania judge who sentenced hundreds of kids to juvenile detention for things as trivial as shoplifting. Many of these kids were first-time offenders who should have been given a slap on the wrist and returned to their normal lives. Instead they were locked up.
Well, guess what? The judge was financially involved with the juvenile detention center. Every conviction was money in his pocket. These kids’ lives were substantially impacted, possibly ruined, due to the corruption of the system. Had they gone to a jury trial, this would have never been possible.
(Some of the details of the above may be innaccurate as I’m too lazy to gather a cite, but the point stands that a jury provides a much-needed check against inappropriate convictions.)
Juries are pro-freedom. They are instructed to rule based on the notion of reasonable doubt. They may not always make the best decisions, and many guilty men have walked free as a result of their ineptitude. However, on the flip side, many innocent men have maintained their freedom due to the protections offered by a jury trial. I’m probably butchering the quote, but as the saying goes, “it’s better to let 100 guilty men walk free than to imprison one innocent man.”