KING HENRY IV
Yea, there thou mak'st me sad and mak'st me sin
In envy that my Lord Northumberland
Should be the father to so blest a son,
A son who is the theme of honor's tongue,
Amongst a grove, the very straightest plant,
Who is sweet Fortune's minion and her pride;
Whilst I, by looking on the praise of him,
See riot and dishonor stain the brow
Of my young Harry. O, that it could be proved
That some night-tripping fairy had exchanged
In cradle-clothes our children where they lay,
And call'd mine "Percy," his "Plantagenet"!
Then would I have his Harry, and he mine.
(1 Henry IV 1.1.78-90)
King Henry, throughout 1 Henry IV, is revealed to be a very religious person, and it is no surprise that religious imagery turns up in this speech ("mak'st me sin in envy") where it provides a snapshot of the king's concerns. Here is a man who relies on religion and God as a pillar of strength in his reign, and who clearly feels that he is the "good guy" in this situation, but it is necessary to remember how he came to power.
I think it is possible that deep down the king recognizes his own guilty hand in the dethroning and indirect execution of Richard II, and therefore he may think that God could seek to punish him for his actions. So he acknowledges the possibility that he is committing a deadly sin (envy) for the otherwise forgivable frustration he feels about Hal. In this he overexerts himself in his religious efforts in order to mollify the God who could be angry with him, an early indication in the play that he is in constant search for forgiveness from the heavens for his actions.
Nathan Rice (SPA '11)