In the Henry IV plays, we watched as Hal learned not just the way of the court but also the way of the world.
In Henry V , Act III, scene 1, we see him put this knowledge into action. As the young warrior king, he urges his men forward but his language is full of acting term. For example he says to "imitate the action," and "disguise fair nature". He has been an "actor" so to speak since we first met him in Henry IV, part 1 and he is now learning a new role. He has not yet experienced the realities of war so his view of war is not real.
By the time we get to Act IV, scene 3 he has seen war and what it can do to people. He has spent the night wondering what gives him the right to ask men to bleed and die for him. The fact that his father became king and he was his eldest son gives him the "legal" right but Henry is more concerned with the morallity of his actions.
His refusal to be ransomed, which would burden the English people, shows that he has become a leader with integrity. His Crispin Day speech is from the heart. No more acting terms. That he offers his men the option of opting out knowing the odds against them were tremendous and that nobody left shows even more what a great leader Henry became. His men believed in him and his leadership and it paid off. The victory at Agnincourt was stunning and Shakespeare's statistics in the play are accurate.
From Act III, scene 1 to Act IV, scene 3, we see a man grow from a rather idealistic warrior king to a war weary but strong king who understands his own mortality. The realities of war have changed him.