Ed Brayton quotes from Scalia during the oral arguments of the Ten Commandments case:
You know, I think probably 90 percent of the American people believe in the Ten Commandments, and I'll bet you that 85 percent of them couldn't tell you what the ten are. And when somebody goes by that monument, I don't think they're studying each one of the commandments. It's a symbol of the fact that government comes -- derives its authority from God. And that is, it seems to me, an appropriate symbol to be on State grounds.
As Brayton notes, this is factually incorrect. The Constitution and the Declaration of Independence make it clear that governments derive their authority from human beings, not from gods. The idea that a government is a divine institution was, in fact, one of the things that the American Revolution was launched to fight against.
From the Constitution:
We the people of the United States, in order to form a more perfect union, establish justice, insure domestic tranquility, provide for the common defense, promote the general welfare, and secure the blessings of liberty to ourselves and our posterity, do ordain and establish this Constitution for the United States of America.
From the Declaration of Independence:
We hold these truths to be self-evident, that all Men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the Pursuit of Happiness -- That to secure these Rights, Governments are instituted among Men, deriving their just Powers from the Consent of the Governed...
Scalia's claim is not only wrong, but deeply immoral because it would mean that people who do not believe in his god are in some fashion outsiders from the political community. It's wrong for the state to declare that the foundation of the government is a set of theological propositions which are not and cannot be accepted by significant religious minorities. Scalia's claim is fit only for a theocracy, not a democratic republic which values religious liberty.