The Archbishop of York instructs Sir Michael to deliver in all haste certain written instructions and information to his allies and relatives who have a substantial number of followers. The archbishop has learned that Hotspur faces the king's power without the support of Northumberland, Glendower, and Mortimer. Convinced that young Percy will be defeated, he knows that the king will then move against him for his part in the conspiracy.
The consensus is that this scene is to be justified solely on the grounds that it looks forward to the main action in 2 Henry IV, wherein royal forces indeed move against the archbishop and Lord Mowbray, his most powerful and dependable ally. Yet there is some reason for its inclusion here strictly with reference to King Henry IV, Part 1. It provides Shakespeare with the opportunity to summarize major events, to foreshadow the rebels' defeat, and to emphasize the seriousness and magnitude of the entire action.
The Sir Michael of this scene does not find a place in history. He may well be a priest, since priests often were given the courtesy title of "Sir."