According to real-world European and American conventions, a military ship's class is usually named after the first (or the leading, or at least one of the earliest) vessel of its kind.
So the Finalizer is the first Star Destroyer of the Resurgent class. The first of the new Resurgent class constructed in violation of treaties with the New Republic I was reading about the Resurgent-class Star Destroyer Finalizer, the First Order's destroyer shown in The Force Awakens, when something struck me as odd.