The Decision
In analyzing the case, Marshall (and the court) examined the Judiciary Act of 1789, which stated that the Supreme Court could "issue writes of mandamus in cases...to any persons holding office under the authority of the United States." The Constitution, the Supreme Court held, confined its original jurisdiction - the ability to hear cases in the first instance - to "all cases affecting ambassadors, other public ministers and consuls, and those in which a state be a party. In all other cases the Supreme Court shall have appellate jurisdiction."
The Court, on 24 February 1803, in a unanimous, 6-0 decision, held that Congress had no power to alter their original jurisdiction in this way and found unconstitutional the Judiciary Act of 1789. The opinion was particularly brilliant because it invalidated an act of Congress yet avoided a direct confrontation with the President because it did not have jurisdiction over the case and thus could not order the Secretary of State to deliver those commissions.
The case established the court's ability to use the tool of judicial review in finding that a staute of action taken by the government is unconstitutional. There is no doubt that the entire judicial system would be helpless without this fundamental ability, and Justice Marshall, although highly criticized for the forum chosen to establish this invaluable tool, in many ways, assured the continuation of America. A judicial system whose sole function is to apply the law without question is not on the same level as a legislature that can make law that goes virtually unchecked. Justice Marshall realized that without judicial review, the courts have no independence from the remaining two branches of government. With the congress deciding the extent of what was constitutional, the contraints placed on the power of the federal government were self imposed and unenforceable.