Article VI, Paragraph 3, US Constitution:
"The Senators and Representatives before mentioned, and the Members of the several State Legislatures, and all executive and judicial Officers, both of the United States and of the several States, shall be bound by Oath or Affirmation, to support this Constitution; but no religious test shall ever be required as a qualification to any office or public trust under the United States."
"In the 1997 case of Silverman v. Campbell the South Carolina Supreme Court ruled that the state constitution requiring an oath to God for employment in the public sector violated Article VI of the federal constitution, as well as the First and Fourteenth Amendments, and therefore could not be enforced.[5] The other seven states still have similar provisions in their constitutions, but they are not enforced in modern times because it is taken for granted they would be held to be unconstitutional if challenged."
http://en.wikipedia.org/wiki/No_Religious_Test_Clause
It seems quite clear -- "no religious test" means exactly what it says. However, the hold-out states (Arkansas, Maryland, Mississippi, North Carolina, Pennsylvania, Tennessee and Texas) are part of the "bible belt" and cherish their anachronisms. So expect no changes to their constitutions.