Do what? Where the health care reform law is concerned...
1. levy taxes.
2. regulate commerce...between the several states.
3. make laws that are necessary and proper in carrying out the foregoing powers.
Therefore, if your point is that the last clause of Art 1, Section 8 is clarative, that all it does is reaffirm all the powers granted to Congress in the preceeding clauses, then to that I would agree to an extend. Still, the mere fact that the Constitution does grant Congress the power to make laws that, in its view, address the overwriting concerns for the nation and can levy taxes to address those concerns where interstate commerce is concerned gives them justification enough. The only question that remains is did Congress overstep its bounds where health care reform, more specifically, the individual mandate, is concerned? Again, I'll leave that to the Supreme Court to decide.