1 – The Declaration contains the appeal to Natural Law as justification for secession(independence).

2 – The Bill of Rights codifies the natural law as they enumerated those rights at the time.

3 – The Constitution describes the organization and processes of the government.

I tend to tell people to read them in that order: Declaration, Bill of Rights, and Constitution: from the reason for the secession: violation of natural law, to the articulation of the specific defenses of it, to the institutions that protect it yet still allow for the production of commons.