It's just to scare all the others. That's what he's doing. At every large protest rally, he would arrest maybe 1% of the participants—very random people—but then the other 99% also feel vulnerable. He thus increases the level of terror and distrust in society. We each have to think a lot about protecting our supporters and we try to do a lot to protect them.
On May 6th, 2021. See this statement in context.