These were the doctrine that all men are created equal, that they are endowed with certain inalienable rights, and that therefore the source of the just powers of government must be derived from the consent of the governed.

From Speech on the 150th Anniversary of the Declaration by Calvin Coolidge.  

When we come to examine the action of the Continental Congress in adopting the Declaration of Independence in the light of what was set out in that great document and in the light of succeeding events, we can not escape the conclusion that it had a much broader and deeper significance than a mere secession of territory and the establishment of a new nation. Events of that nature have been taking place since the dawn of history. One empire after another has arisen, only to crumble away as its constituent parts separated from each other and set up independent governments of their own. Such actions long ago became commonplace. They have occurred too often to hold the attention of the world and command the admiration and reverence of humanity. There is something beyond the establishment of a new nation, great as that event would be, in the Declaration of Independence which has ever since caused it to be regarded as one of the great charters that not only was to liberate America but was everywhere to ennoble humanity.

It was not because it was proposed to establish a new nation, but because it was proposed to establish a nation on new principles, that July 4, 1776, has come to be regarded as one of the greatest days in history. Great ideas do not burst upon the world unannounced. They are reached by a gradual development over a length of time usually proportionate to their importance. This is especially true of the principles laid down in the Declaration of Independence. Three very definite propositions were set out in its preamble regarding the nature of mankind and therefore of government. These were the doctrine that all men are created equal, that they are endowed with certain inalienable rights, and that therefore the source of the just powers of government must be derived from the consent of the governed.

If no one is to be accounted as born into a superior station, if there is to be no ruling class, and if all possess rights which can neither be bartered away nor taken from them by any earthly power, it follows as a matter of course that the practical authority of the Government has to rest on the consent of the governed. While these principles were not altogether new in political action, and were very far from new in political speculation, they had never been assembled before and declared in such a combination. But remarkable as this may be, it is not the chief distinction of the Declaration of Independence. The importance of political speculation is not to be underestimated, as I shall presently disclose. Until the idea is developed and the plan made there can be no action.

It was the fact that our Declaration of Independence containing these immortal truths was the political action of a duly authorized and constituted representative public body in its sovereign capacity, supported by the force of general opinion and by the armies of Washington already in the field, which makes it the most important civil document in the world. It was not only the principles declared, but the fact that therewith a new nation was born which was to be founded upon those principles and which from that time forth in its development has actually maintained those principles, that makes this pronouncement an incomparable event in the history of government. It was an assertion that a people had arisen determined to make every necessary sacrifice for the support of these truths and by their practical application bring the War of Independence to a successful conclusion and adopt the Constitution of the United States with all that it has meant to civilization.