Some of those that work forces

Are the same that burn crosses

They're saying that some of the people in powerful positions are racists who burn crosses. Burning crosses is a KKK harassment activity where they erect and burn a cross on the lawn of a black person's home while wearing masks to hide their true identity. Essentially they're alluding to systemic racism.

(It is a Rage Against the Machine lyric from 'Killing in the Name')

I've had their discography on repeat for a couple weeks now, very much recommend

The police forces

I can't find a source for this at the moment, but I read somewhere that the original line was "Some of those that hold office/are the same that burn crosses." It rhymes a lot better.