Why is the Declaration of Independence important to us now and during the revolutionary war?

The United States Declaration of Independence is one of the most important founding documents of the American system of government. While the Declaration justified colonial America's quest for independence from Great Britain, it also proposed a formula for self government based on the fundamental (i.e., natural) rights of humankind.  The most profound statement of the Declaration that carries as much weight today as it did in 1776 is the idea that "all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness." Every person, regardless of any perceived difference from another person, has the same basic rights. No one, not even the government, has the right to take away the rights all people were born with -- the right to life, the right to be free (with certain limitations for illegal activity), and the right to have the necessities of life that bring happiness. 

The second most important statement is that "Governments are instituted among Men, deriving their just powers from the consent of the governed,—That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it." Democratically elected governments can become oppressive just as authoritarian governments like that of George III tended to be. Therefore, the founders saw fit to insist on the right to "alter" or change the existing government to insure that those in power protected the rights of the governed. Today, we don't change our government via revolutionary wars, we do so at the polls when we vote to put a new president, congressional members, or even local leaders in office. The Declaration not only says it is the right of the people to do this, it says "it is their right, it is their DUTY, to throw off such Government, and to provide new Guards for their future security."

The ideas in the United States Declaration of independence are as important today as they were in 1776 even though we live in totally different country from the one that emerged following the American war for independence. Many colonial Americans felt George III's new laws governing the colonies were oppressive.  In today's America we find, at any given time, that many feel the same way about the leaders of this country, that they are not looking out for the rights of the people, i.e., the governed. The Declaration of Independence admonished the governed to be prudent, i.e., not hasty but careful or wise, when overthrowing an existing government by saying, “Prudence, indeed, will dictate that Governments long established should not be changed for light and transient causes.” Only once in almost 240 years of existence, between 1861-1865, have the people of the U.S. determined that it was justifiable to go war to protect the natural rights of persons living in this country. Though passionate and often heated, most  disagreement with the way government carries out its purpose has been "light and transient" enough to be altered through elections and the understanding that elected officials serve with the consent of the people.