“Statement on the verdict in Kyle Rittenhouse trial”

Common Council President Cavalier Johnson November 19, 2021

“Today’s verdict in Kenosha shows that the arc toward justice is still bending.”

https://city.milwaukee.gov/ImageLibrary/Groups/ccCouncil/News/2021/District-02/11_19StatementontheVerdictinKyleRittenhouseTrial.pdf

What does “The arc of justice is still bending” mean?