The presence of a storm in Shakespeare's plays tends to reflect rage or foreshadow a catastrophe. The threatening, destructive weather on that "fearful night" reflects the dark and dangerous mood of the play. The object of the conspiration to take place is the assassination of Julius Caesar in the hands of Brutus.
Your keyword is "nonessential" which means you don't need it. So the statement is true a nonessential element is not necessary for the meaning or the structure of the sentence.
