What does Sessions being fired mean?

It means that Trump didn't want Sessions fired before the election because he would have lost millions of votes if he had done that before the elections. So, it was a way of deceiving Trump voters by doing this.

2nd it means that Trump wants Whitaker (acting Attorney General) in who has said he would defund Mueller on TV already if he was put in as Attorney General. So, likely Whitaker will not make Mueller's report public ever  to the Congress or the American people and everything will be hidden in a complete coverup by Trump and Whitaker now.

So, an injustice is being perpetrated upon the American people starting right now by Trump starting with the Firing of Sessions.