The assignment was the promotion of the sovereignity of England, and inspiration to unite and fight for it, to stand against invasion of a conqueror:
This England never did, nor never shall,
Lie at the proud foot of a conqueror,
But when it first did help to wound itself.
Now these her princes are come home again,
Come the three corners of the world in arms,
And we shall shock them. Nought shall make us rue,
If England to itself do rest but true.
--King John – Act 5, Scene 7
And you, good yeoman,
Whose limbs were made in England, show us here
The mettle of your pasture; let us swear
That you are worth your breeding; which I doubt not;
For there is none of you so mean and base,
That hath not noble lustre in your eyes.
I see you stand like greyhounds in the slips,
Straining upon the start. The game's afoot:
Follow your spirit, and upon this charge
Cry 'God for Harry, England, and Saint George!'
--Henry V – Act 1, Scene 2
Her words were these.
"My loving people, we have been persuaded by some that are careful of our safety to take heed how we commit ourself to armed multitudes for fear of treachery; but I assure you, I do not desire to live to distrust my faithful and loving people. Let tyrants fear. I have always so behaved myself that, under God, I have placed my chiefest strength and safe guard in the loyal hearts and good will of my subjects, and therefore I am come amongst you, as you see, at this time, not for my recreation and disport, but being resolved, in the midst and heat of the battle, to live or die amongst you all, to lay down my life for my God and for my kingdom and for my people, my honour, and my blood, even in the dust. I know I have the body of a weak and feeble woman, but I have the heart and stomach of a king, and a king of England too, and think foul scorn that Parma or Spain, or any prince of Europe should dare to invade the borders of my realm; the which, rather than any dishonour shall grow by me, I myself will take up arms, I myself will be your general, judge, and rewarder of every one of your virtues in the field. I know, already for your forwardness, you have deserved rewards and crowns; and we do assure you, in the word of a prince, they shall be duly paid you. In the meantime my lieutenant-general shall be in my stead, than whom never prince commanded a more noble or worthy subject, not doubting but by your obedience to my general, by your concord in the camp, and your valour in the field, we shall shortly have a famous victory over those enemies of my God, of my kingdom, and of my people."
http://tudorhistory.org/primary/tilbury.html
As for Shakespeare's stirring and patriotic themes and language, without a direct link to the highest levels of governmental policy (the author known to be Edward de Vere, 17th Earl of Oxford, Lord Great Chamberlain of England), the origin of this propaganda as a self-serving instrument of government, disappeared.