The core philosophy of Libertarianism is based on the idea that your rights as an individual are not determined by the state or through the democratic process but are derived from God or the natural universe. One does not necessarily need to accept God to arrive at this (Many of the founding fathers were Deists). You can simply accept the secular notion that you own yourself and through the process of logic and the acceptance of universal first principles i.e don’t rape, assault, steal, or commit fraud, you will arrive at the same conclusion.
This is the basis for the Declaration of Independence explained in the quote:
‘“We hold these truths to be self-evident, that all men are created equal and endowed by their creator with certain unalienable rights including life, liberty, and the pursuit of happiness.”
The philosophy holds that humans have absolute natural rights (in the sense of universal rights that are inherent in the nature of ethics, and not contingent on human actions or beliefs). The theory, espoused by Thomas Hobbes and John Locke among others, laid the foundation for the U.S Constitution, originating with the concept of natural justice or natural right of Socrates, Plato and Aristotle.