Why did George Washington have "The Crisis" by Thomas Paine read to his troops?

In "The Crisis No.1," Thomas Paine begins by setting the stakes of the fight for American independence. The first paragraph begins,

THESE are the times that try men's souls: The summer soldier and the sunshine patriot will, in this crisis, shrink from the service of his country but he that stands it NOW, deserves the love and thanks of man and woman. Tyranny, like hell, is not easily conquered; yet we have this consolation with us, that the harder the conflict, the more glorious the triumph. What we obtain, too cheap, we esteem too lightly:—'Tis dearness only that gives every thing its value.

Paine sets the stage for the severity of the time in which they are living. He notes that many people would "shrink from" the job of defending his land and his people. He refers to those people as "sunshine patriots," meaning they are only loyal to the country when it is easy to do so (like a "fair-weather fan" only cheers on a team when it's winning). The men who would be fighting with Washington are not those kind of patriots; they are more loyal and more noble. This opening would assure them that they are just and are fighting for a moral cause. Paine reminds them that it's not easy to overcome "Tyranny" but that all things worth winning come at a price.

Later in the pamphlet, Paine makes a more explicit call to action that could be seen as a strong motivator to Washington's troops. Paine exclaims,

I call not upon a few, but upon all; not on THIS state or THAT truth but on EVERY state; up and help us; lay your shoulders to the wheel; better have too much force than too little, when so great an object is at stake. Let it be told to the future world, that in the depth of winter, when nothing but hope and virtue could survive, that the city and the country, alarmed at one common danger, come forth to meet and to repulse it. Say not, that thousands are gone, turn out your tens of thousands; throw not the bur hen of the day upon Providence, but "Shew your faith by your works," that God may bless you. It matters not where you live, or what rank of life you hold, the evil or the blessing will reach you all. The far and the near, the home counties and the back, the rich and the poor, shall suffer or rejoice alike.

Here, Paine hopes to rally as many as possible to the revolutionary cause; similarly, Washington would want to rally his soldiers behind this cause again before charging into battle. He assures the soldiers that they will be blessed for their loyalty and their sacrifice. Soon after this section, he says that those who do not fight for the country will "curse" his children with his "cowardice," that this choice to fight or not to fight will have repercussions throughout the generations. This would give the soldiers extra motivation to make their families proud and to hopefully ensure a brighter future for their children.

Paine ends the pamphlet talking about fear. He claims that he does not fear because he feels God is on his side and that he is speaking out for justice and truth. The soldiers fighting in the war would feel reassured to hear such a sentiment, as it would be totally natural for them to fear the upcoming battles and their possible outcomes. Overall, "The Crisis No.1" reminds soldiers why they are fighting and appeals to their sense of justice and morality.

George Washington would have had "Number 1" of The American Crisis read to his troops to help motivate them and encourage them to continue the fight. Thomas Paine's The American Crisis discusses some of the hardest parts of the war, and would have reminded the soldiers of their dedication to the American cause. The quote from the reading,

"Tyranny, like hell, is not easily conquered; yet we have this consolation with us, that the harder the conflict, the more glorious the triumph."

would have reminded the soldiers that if they pushed onward and won, their victory would be much sweeter due to their struggles. This quote also serves to kindle hope in the soldiers. Even though they had lost battles and been pushed back, they should not assume all was lost and give up their fight.

Washington also choose to have part of The American Crisis read to his soldiers because the language would be familiar to them. Paine's writings used vocabulary that would be easy to understand by Washington's men.

Why did George Washington have the first essay in The Crisis read to his troops?

The reason Washington would do this was to raise the morale of his soldiers.

The first essay in The Crisis was dated December 23, 1776.  This was one of the darkest times in the Revolutionary War.  Washington and his army had been pushed out of New York and through New Jersey.  They had ended up in Pennsylvania, very discouraged.  Even the Continental Congress, which was the US government at the time, had been forced to run away from the British army.

In this context, it seemed that the Revolution might well be over.  Washington would have needed a way to encourage the men to continue fighting.  One way to do that would have been to read Paine's work to them.  This essay is a very powerful statement of why it is important not to give up the fight.  It does things like encouraging the men to keep fighting because their victory over tyranny will be glorious.

Tyranny, like hell, is not easily conquered; yet we have this consolation with us, that the harder the conflict, the more glorious the triumph.

Because of the fact that it was inspirational, Washington would have wanted his soldiers to hear it.