It could be that the most important part of Justice Roberts's opinion is the seven page introduction (I say that perhaps because I haven't had time to digest the rest). But the introduction reminds us that the courts have a limited but important responsibility:
Members of this Court are vested with the authority to interpret the law; we possess neither the expertise nor the prerogative to make policy judgments. Those decisions are entrusted to our Nation’s elected leaders, who can be thrown out of office if the people disagree with them. It is not our job to protect the people from the consequences of their political choices.(slip opinion at p. 6) Before getting to that, and perhaps even more importantly, Justice Roberts reminds us that ours is a government of limited powers. This is what makes our country almost unique in the world. Most governments, even most democratic governments, start from the proposition that the sovereign (in most cases that is or used to be the king) has unlimited powers. In a parliamentary democracy, the sovereign might delegate those powers to a legislature, but they are still essentially unlimited, and they are still powers that are derived from the top down: from God, to the King and then to the legislature. Our government is premised on the opposite principle. Our government started by overthrowing the king, and declaring that the people are sovereign. That is why the Constitution starts with the words, "We the People." All power is retained by the people, or by their state governments, and the federal government possesses only the powers that we the people have expressly granted to it in the Constitution. This is our founding principle. It might be the only principle that we can all agree on.
Yet we never seem to agree on that principle in practice, because our views regarding the scope of the federal government's powers, change depending on what the government wants to do. Whichever party (and parties, remember are a concept that are foreign to our Constitution, and don't fit comfortably within our founding principles) obtains power wants the government to have all the power it needs to do whatever it is that that party supports. The opposition, on the other hand, the party out of power, tends to think of everything the government does that the opposition doesn't like, as beyond its power. This is why we are constantly arguing about the Constitution, and why the Supreme Court plays such an important role in our system of government, unlike many other governments. This is why everything new that the federal government tries to do, whether it is levying an income tax, or building roads, or monitoring our private lives, or involving itself in schools or social welfare programs, presents such a struggle. And this is why Chief Justice Roberts has to spend the first few pages of the Court's decision giving us a history and civics lesson before he can decide the question.
Chief Justice Roberts deserves enormous praise for his courageous decision today. Upholding the Affordable Care Act probably violates his personal policy preferences, and tests the limits of his personal views of the scope of the federal government's power to to enact such a law. Moreover, the Chief Justice had to vote on the signature legislative achievement of a president from the opposite party, a president who even voted as a senator against Chief Justice Roberts's own confirmation! (Now there's a vote President Obama would probably like to take back today.) Despite the intensity of Justice Roberts's personal feelings, and his knowledge that henceforth and to the end of his days, he will probably be vilified and denounced as a traitor by the right, the Chief Justice was able to put those feelings aside and uphold our founding principles. The Chief Justice proved that the Court is not a purely partisan institution that simply approves or disapproves legislation based on its personal policy preferences, and he thereby upheld the integrity and dignity of the Court and the Constitution. Hail to the chief!