Words memorized in 8th grade civics

We hold these truths to be self-evident, 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.
The Declaration of Independence

We the people of the United States, in order to form a more perfect union, establish justice, insure domestic tranquility, provide for the common defense, promote the general welfare, and secure the blessings of liberty to ourselves and our posterity, do ordain and establish this Constitution for the United States of America.
Preamble, United States Constitution

... that this nation, under God, shall have a new birth of freedom — and that government of the people, by the people, for the people, shall not perish from the earth.
Lincoln's Gettysburg Address

The Declaration is a formal apologia: a defense especially of one's opinions, position, or actions.

When in the Course of human events it becomes necessary for one people to dissolve the political bands which have connected them with another and to assume among the powers of the earth, the separate and equal station to which the Laws of Nature and of Nature's God entitle them, a decent respect to the opinions of mankind requires that they should declare the causes which impel them to the separation.
[emphasis added to stress the apologetic nature of the document]

The legal status of the Declaration is interesting. From the British Parliament's perspective it has no legal standing - the Colonists have not the legal competence to declare themselves independent of Great Britain. The Continental Congress itself asserted no legal authority over the several States. The Declaration, after the rousing and memorable introduction which we all presumably learned by heart at some point during our education, is phrased as a legal tort against King George III - it is extremely dry reading. No one is likely to quote from memory any of the specific charges brought against George III. It is, and is best understood as, a formal apologia.

The Preamble introduces the legal document which follows. Of the three quotations, only the Preamble is directly relevant to legal foundation of the United States. It is the Framers' "mission statement", explaining the origin, scope, and purpose of the Constitution.

Lincoln's Gettysburg Address is a speech - one of the most quoted speeches in U.S. history. It has no legal standing. Strangely, however, the phrase, "government of the people, by the people, for the people" is frequently assumed to derive from the Constitution! (Recent NYT "Letters to the Editor" confirm this.) Perhaps owing to its brevity and conciseness, this phrase has assumed a popular quasi-legal status, as defining the nature of the United States government.

As noted above, the Declaration is the oddest of these three "founding" documents. The opening paragraph is a single 71-word sentence!

To emphasize the Declaration's oddness, I'd like to examine what is perhaps its most well-known clause:

We hold these truths to be self-evident

"We" - presumably the Continental Congress, and perhaps by extension the people of the [lowercase]united States whom they represent - "hold these truths to be self-evident." Note: simply by asserting that "We hold these truths to be self-evident" suggests that others may not! What kind of self-evident truths are these, that they are subject to debate, and that we must make known whether or not we accept them?

A quick look at the "self-evident" truths reveals that they are anything but!

that all men are created equal

Libraries have been written regarding the truth-value of this "self-evident" truth - what, exactly, is being asserted here? This was - and is - a revolutionary concept!

that they are endowed by their Creator with certain unalienable Rights

This is particularly tricky. The Congress wants to assert something like "the rights of man", but are shrewd enough to realize that, under common law, rights are things granted by lords to vassals - rights derive from relationships. How to overcome this logical difficulty? Ah! Our "rights" are endowed us by our Creator! The term "Creator" - instead of, say, "our G-d" - was probably sufficiently neutral to satisfy the Deists!

that among these are life, liberty, and the pursuit of happiness

Locke's Second Treatise on Government cites "life, liberty, and property" as inalienable rights. The Founders shied away from "property" for a variety of contrasting and contradictory reasons - "the pursuit of happiness" was sufficiently wishy-washy to satisfy all!

Of the three documents cited, only one has legal standing: The Preamble of the United States Constitution. It is the Constitution which is the law of the land! It is the Constitution which all "Senators and Representatives... and the members of the several state legislatures, and all executive and judicial officers, both of the United States and of the several states" are bound by oath to support (Article VI).