The Preamble was placed in the Constitution more or less as an afterthought. It was not proposed or discussed on the floor of the Constitutional Convention. Rather, Gouverneur Morris, a delegate from Pennsylvania who as a member of the Committee of Style actually drafted the near-final text of the Constitution, composed it at the last moment. It was Morris who gave the considered purposes of the Constitution coherent shape, and the Preamble was the capstone of his expository gift. The Preamble did not, in itself, have any substantive legal meaning. The understanding at the time was that preambles are merely declaratory and are not to be read as granting or limiting power - a view sustained by the Supreme Court in Jacobson v. Massachusetts (1905).
The Heritage Guide to The Constitution - Edwin Meese III; page 43