At the Archbishop of York's palace in York, the Archbishop gives some messages to Sir Michael Vernon for delivery to the Lord Marshal, and to the Archbishop's cousin, Scroop. The archbishop, who is on the side of the rebels, seems convinced that the King's forces will prove too strong for Hotspur's. The Archbishop knows that if Hotspur fails, the King will then pay him, the Archbishop, a visit, since he knows the cleric is in league with the rebels. The Archbishop sends the letters in order to round up some support for himself.
Act 3 scene 3 shows more dissension amongst the leaders of the rebels. (No dissension is shown in the King's camp, which suggests there is a greater spirit of unity among those who favor the King's cause.) Worcester and Vernon exercise common sense and caution, wanting to delay the battle, but Douglas and Hotspur, the two excitable and impulsive warriors, win the argument.
The scene is important because it provides, in Hotspur's long speech, a summing up of the reasons the rebels are going to war. Hotspur spends far more time describing his resentment at how ungrateful the King has been to the Northumberland family after they helped him to the throne than he does in describing any offenses the King may have committed against the national interest. There is certainly a fair amount of personal spite that is motivating the rebels.