And that is his opinion. But it does not establish a state religion because it is there. If you put a Montana state flag in an Indiana courtroom, it doesn't change the state. The monument did not establish a religion. It's merely a common philosophy. Some may revere it. Some may not. It's only a problem if people are forced to worship it.
1) the laws of God as stated in the Ten Commandments are superior to any other law;
2) what (the words) he has chiseled on his monument comes from God;
3) he derives his secular judicial powers from God;
4) no other religious statements may be made there, only his.