Madison's explanation of the BoR
Gunshowontheweb has the Annals of Congress where Madison explained to the House his rationale for a Bill of Rights.
"I should be unwilling to see a door opened for a reconsideration of the whole structure of the Government--for a re-consideration of the principles and the substance of the powers given; because I doubt, if such a door were opened, we should be very likely to stop at that point which would be safe to the Government itself. But I do wish to see a door opened to consider, so far as to incorporate those provisions for the security of rights, against which I believe no serious objection has been made by any class of our constituents: such as would be likely to meet with the concurrence of two-thirds of both Houses, and the approbation of three-fourths of the State Legislatures.... I know some respectable characters who opposed this Government on these grounds; but I believe that the great mass of the people who opposed it, disliked it because it did not contain effectual provisions against encroachments on particular rights, and those safeguards which they have been long accustomed to have interposed between them and the magistrate who exercises the sovereign power; nor ought we to consider them safe, while a great number of our fellow-citizens think these securities necessary."