Here we see the clash between Kent and Oswald outside Gloucester's castle. Kent has arrived, following Cornwall and Regan, in advance of Oswald who has straggled behind. They all left Cornwall's together.
Kent recognizes Oswald, but Oswald doesn't recall Kent, or at least doesn't want to! Kent rails against Oswald repeatedly calling him a cowardly "knave" in the longest character description in all Shakespearean plays. From this section we can see that Oswald is a "young" "boy". He is a made up gentleman - tailor made.
Kent is annoyed that Oswald's purpose is succeeding at his master's expense, and so he wants to fight Oswald. But Oswald will not draw his sword against this "ancient ruffian."
Oswald's loud cries are heard in the castle and Edmund, Cornwall, Regan, and Gloucester come out to break up the fight. Kent explains the reason for the fight and ends up insulting Cornwall and Regan so much that he is put in the stocks.
After little more than a week, supposedly away in France, Cordelia has heard of her sisters' evil towards their father, has learned of the disguise of Kent and sent him a letter assuring him that she will "give losses their remedies." Kent uses the word "miracle" to describe his receipt of this letter. Anyone who had seen Cordelia disguised as the Fool would see the reason for the "miracle"!