Bert's the poor (but smart) sap at the center of all this controversy. He's a schoolteacher who decided to teach Darwin's theory of evolution in his public school classroom, even though it's against the law to do so. This seemingly small decision has landed him in the slammer.
But that's not all. Whether Little Old Bert expected to garner a lot of attention or not, news of his trial really picks up momentum. Because really, the trial isn't about Bert at all—it's about the definitions of freedom of religion etc., the separation between church and state, and all of that other serious, Constitutional-type business.
To put it bluntly, the whole nation is watching this trial. And this was back when television was kind of a new deal, so. Be impressed.
Anyway, here's Bert's explanation as to why he thinks teaching his students about evolution is the right thing to do:
You know why I did it. I had the book in my hand, Hunter's Civic Biology. I opened it up, and read my sophomore science class Chapter 17, Darwin's Origin of Species. (RACHEL starts to protest) All it says is that man wasn't just stuck here like a geranium in a flower pot; that living comes from a long miracle, it didn't just happen in seven days. (I, I, 130-135)
When Rachel protests, he explains that ideas and actions are not simply good or bad:
It isn't as simple as that. Good or bad, black or white, night or day. Do you know, at the top of the world the twilight is six months long? (I, I, 139-41)
These passages show us that Cates is a thinking man. He doesn't just do what other people tell him to, without thinking things through first. Dude can't accept that the Bible is a completely literal document. And since he's decided that teaching evolution in schools is morally correct, according to his internal compass, then he's not going to follow some silly law that states otherwise.
This isn't to say that right and wrong aren't really important to Bert; clearly, they are. But Bert's smarty-pants attitude is a big part of the play's overall message, because by silencing one of the cleverest guys in town, his enemies are basically positioned as people who want to keep everyone ignorant.
They're like walls who won't budge in the face of progress. And Bert's just your average Joe saying, Hey, guys, we should move. Just a little. Come on. It won't hurt. The water's fine.
Bert gets pretty scared during the trial, as he starts to realize he might be looking at a future full of group showers and cellmates who killed their grannies. But he sticks to his guns. He turns out to be a pretty courageous guy, even if he's not as showy as the lawyers.
After he's found guilty, Bert explains what it is, exactly, that he wants:
I was a schoolteacher. (With difficulty) I feel I am…I have been convicted of violating an unjust law. I will continue in the future, as I have in the past, to oppose this law in any way I can. (III, 256-70)
Even though Bert sometimes seems like a small-town pawn in big-time players Drummond and Hornbeck's game, Bert really isn't so simple as that. Bert is willing to swim against the tide of his town, so to speak.
And his status as on outsider contributes to the play's overall themes because, throughout history, revolutionary new ideas have often come from the fringes. Ideas like: the earth is round, the sun is at the center of the universe, you can wear white after Labor Day. At one time or another, people have thought that all of these concepts were totally batty.
So, yes, Drummond and Hornbeck are using Bert's trial to grandstand—to heat up the controversy over Darwin's ideas and, eventually, get that law against teaching evolution changed. But Bert clearly believes in what he taught.
Plus, at a higher level, you could say that it's really the playwrights who are using Bert. They're telling this story in order to spotlight those brave souls who face punishment for standing up for what they believe in. And you've gotta appreciate what they did here, because defending free thinkers was a dangerous thing to do in 1955.