Having scorned the power of Rome before, John now submits to its authority in hopes that Pandolf will be able to hold off the invaders. (Given the religious and political climates of Shakespeare's time, this act is--as the Bastard comprehends--a clear statement of John's uncertainty and weakness; if he was ever an impressive or powerful figure, he is now suffering a quick decline.) Like John's effort to win back his nobles by reporting that Arthur was not murdered, this ploy comes too late to have the desired result. Louis too resists the authority of Rome now that he is so close to gaining the throne and continues his attack.
The Bastard demonstrates an extraordinary ability to bluff when he threatens Louis, insisting that John's army is so enormous that it will completely annihilate Louis' forces. He describes the destruction that will be wrought; but Louis is shrewd enough not to believe him. Unfortunately for Louis, he should listen to the Bastard: While it is true that John's army is not as large as the Bastard claims, Louis's forces will soon be shipwrecked--yet again--and decimated at sea.