The above quotation comes from the inestimable, Thomas Jefferson, in a letter he wrote to James Madison, considered to be the author of the Constitution, of which this letter was written to James Madison, before the Constitution was submitted and subsequently ratified by the necessary amount of States. Clearly, as the Constitution does contain the Bill of Rights, Thomas Jefferson's viewpoint was not only considered, but implemented, which was and still is a great gift to the people of this republic.
The Constitution was written to specifically enumerate the delegated rights that are provided by the consent of the people to that government of, by, and for the people of the United States of America. The Bill of Rights, on the other hand, is to enumerate specifically the rights of the people in regards to that government, as well as to stipulate clearly that rights not explicitly delegated by that Constitution to that government are reserved to the people of the United States of America.
So then, the purpose and importance of the Bill of Rights is so that the people, are not subsumed by a government that becomes a law and a force itself; for if and when that happens, than surely this is not a government operating any longer under the consent of the governed, but rather would appear to be a government that is operating outside the need of that consent, and therefore it is up to the people to see that such a government as that, be recognized as being in violation of that highest law of the land, its Constitution.
It is the Bill or Rights that makes it clear that the Constitution was not written to set up a government, apart from the people, or a government that would be above the people, but rather it was created so as to prevent that government from aggrandizing unto itself powers that would make it a law of its own, and effectively thereof, separate from the people, so that the people thereby would become inferior to and hence subservient to that government. After all, the very purpose of a people banding together into one civil government, is for that government to be of service to that people, and to the degree that it is not, that government is not a legitimate government of, for, and by the people.
A government that is not accountable to the people, is not the government that the Constitution, with its incumbent Bill of Rights, was created to be. The Bill of Rights is necessary to remind that government, that all of the people have been created with unalienable rights, and that these rights are not given by that Constitution, but rather by their Creator, of which these people are forever entitled to their free will, their free conscience, their freedom of movement, their freedom of assembly, their freedom of the press, their freedom to worship, and their liberty to be about their business, without having to give notice to that government, or to receive permission by that government to do so.
The Bill of Rights makes it clear that the legitimate function of our national government is to establish justice for all, and to promote the general welfare for the people, and by doing so, that government serves well its people.