"I can call spirits from the vasty deep..."
See in text (Act III - Act III, Scene 1)
In this context, "vasty deep" presumably refers to the underworld and the spirits of the dead. The Welsh rebel Glendower and Henry Percy (Hotspur) have not been getting along, mostly due to their conflicting personalities and their penchant for self-aggrandizement. While they plot against Henry IV, Hotspur jeers at Glendower for his wildly exaggerated claims to summon and control the devil and other spirits. Hotspur can easily tolerates his own brags and bravado, but notice how he can't tolerate another's.
"The better part of valour is discretion; in the which better part I
have saved my life..."
See in text (Act V - Act V, Scene 4)
Falstaff's famous phrase, most often quoted today as "Discretion is the better part of valor," somewhat redeems his cowardly act. He has just risen from his feigned death having playing dead on the battle field to escape true death. Falstaff claims that concepts like "honor" and "valor" help no one if one's dead, and so he excuses his actions as the kind of "discretion" that keeps someone from foolishly putting oneself into harms way in order to cultivate a reputation for heroism. If such actions keep you alive, then it's not counterfeiting, but a genuine "image of life."