This is a great question. This question can be answered in many different ways. So, there will be differences of opinion. I think one of the best ways to answer this question is by looking a what the Declaration of Independence, which leads up to the Constitution, states. The opening sections states:
"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."
These words alone provide an incredible basis for freedom and liberty. Think of some of the points and the implications. First, men are created equal. Second, they are endowed with unalienable right by their creator - the pursuit of life, liberty, and happiness. Third, the document grounds these points in a divine being. Moreover, it states that they points do not even need proof, because they are self-evident. The implications guard and protect freedom.