GAUNT                        God in thy good cause make thee prosperous!

Be swift like lightning in the execution

And let thy blows, doubly redoubled,

Fall like amazing thunder on the casque

Of thy adverse pernicious enemy.

Rouse up thy youthful blood, be valiant and live.

BOLINGBROKE          Mine innocence and Saint George to thrive! (1.3.78-84)

It’s clear where Bolingbroke gets his eloquence and rhetorical force, as well as his valour: this is old Gaunt, right in there, evoking speed, strength, motion. He gives his blessing, yes: God in thy good cause make thee prosperous—no misgivings about who is in the right, or any gesture at neutrality. Go on my son. Execution here means the execution of this particular action, but of course it also suggests that Bolingbroke is going to execute Mowbray, as an agent of divine justice and vengeance; to imagine execution as swift like lightning evokes the flash of a blade, streaking through the air, and then Gaunt supplies the sound effects, the amazing thunder, stupefying, befuddling, rained down on Mowbray’s helmet, not merely redoubled (picking up the play with doubles from Bolingbroke’s speech) but doubly redoubled. Bolingbroke is to beat a tattoo of blows on Mowbray’s head, so fast and forceful that he won’t know what’s hit him. But Gaunt doesn’t even deign to name Mowbray: he’s simply thy adverse pernicious enemy. He does, however, indirectly admit his age, by invoking his son’s youthful blood, which must be roused, heated: be valiant and live! he exhorts him (and there’s a hint of paternal anxiety in those final words, yes, be victorious, be courageous—but above all, live.) Bolingbroke picks up the sentiment like a baton: he will thrive (probably closer to live than the half-rhyme, or eye-rhyme, that we might notice now) in his innocence, the knowledge of the righteousness of his cause, and with the help of Saint George, England’s patron saint. This is, somehow, a fight for the future of England.