the founders believed in natural rights. They premised the constitution on that and intended a federal government limited to the specific powers delegated it. A conflict arose between the "federalists" and the anti federalists because one group wanted guarantees of the inalienable rights they all believed in and to them merely NOT delegating a power to the federal government was not enough to alleviate their fears. so the bill of rights was established and as the USSC noted in Cruikshank, the right to keep and bear arms pre-existed the Bill of rights and was merely recognized by it. the commerce clause says nothing about congress having power over retail commerce between individuals and FDR ignored the clear language of the CC to "find additional powers"
this is all pretty much standard first year constitutional law stuff