I never thought to hear you speak again.
Thy wish was father, Harry, to that thought.
I stay too long by thee; I weary thee.
Dost thou so hunger for mine empty chair
That thou wilt needs invest thee with my honors
Before thy hour be ripe? O foolish youth,
Thou seek'st the greatness that will overwhelm
Stay but a little; for my cloud of dignity
Is held from falling with so weak a wind
That it will quickly drop. My day is dim.
Thou hast stolen that which after some few hours
Were thine without offense, and at my death
Thou hast sealed up my expectation.
Thy life did manifest thou lovedst me not,
And thou wilt have me die assured of it.
Thou hid'st a thousand daggers in thy thoughts,
Which thou hast whetted on thy stony heart
To stab at half an hour of my life. (4.3.244-262)
In one of the play's most striking moments, Prince Hal, thinking his father has died, takes the royal crown and leaves the room. When the king wakes up from his nap, he's ticked and goes off on his son, accusing Hal of hiding a "thousand daggers" in his "thoughts." In other words, Henry has always suspected that Hal doesn't love him and wants to see him dead so he, Hal, can get his hands on the crown. (Apparently, Henry has forgotten all about how Hal saved his life during battle in act five of Henry IV Part 1.)
This passage speaks to the delicacy of lineal succession and the consequences of primogeniture (the system by which eldest sons inherit their fathers' wealth, titles, lands, power, debt, etc.). As long as one's father is alive, a son has limited power and wealth, which can strain even the best father-son relationships. Shakespeare explores the idea that all sons (not just princes who stand to inherit kingdoms) inevitably look forward to their fathers' deaths in other plays as well – particularly Hamlet and King Lear.
We also want to point out Henry's witty remark that Hal "fathered" the idea that King Henry was dead. In other words, Henry claims that Hal "wish[ed]" his father was dead and, was therefore, quick to imagine that the old man had passed away when, in fact, he was only sleeping.