“فَ” (fa)This word resumes the flow after a pause or change in thought.Corpus grammarREM — prefixed rem particle.
“فِرُّ” (firru)means “So flee” in this verse. It is a verb. an action or state word. Here it is second person — masculine — plural.Corpus grammarV — second person masculine plural imperative verb.
“وا” (wā)an attached pronoun meaning “you all.” It shows who is being addressed.Corpus grammarPRON — second person masculine plural subject pronoun.