The Story: In 2010, voters in Oklahoma passed a legislatively referred constitutional amendment that would prohibit state courts from using international law or Sharia law when making rulings. But last Thursday, a federal judge ruled the amendment violated religious freedoms granted by the U.S. Constitution.

The Background: Sharia is the moral code and religious law of Islam that deals with topics  ​addressed by secular law, including crime, politics, and economics, as well as personal matters such as sexual relations, hygiene, diet, and prayer. The two primary sources of Sharia law are the Quran and the example set by the founder of Islam, Muhammad. The introduction of Sharia across the globe is a longstanding goal for Islamist movements.

In her ruling the judge wrote that “it is abundantly clear that the primary purpose of the amendment was to specifically target and outlaw Sharia law and to act as a preemptive strike against Sharia law to protect Oklahoma from a perceived ‘threat’ of Sharia law being utilized in Oklahoma courts.”

Why It Matters: Opposing Sharia law may appear to be commonsensical measure. But there is a compelling reason why Christians should join in rejecting anti-Sharia legislation: By helping to push the idea that religious beliefs should be kept private, anti-Sharia laws are a threat to all of our religious liberties. As the Catholic legal scholar Robert K. Vischer explained last year in First Things:

Though popular with secularists and religious conservatives, anti-Sharia legislation does not defend against theocracy but calls into question our society’s fundamental commitments to meaningful religious liberty and meaningful access to the courts. These commitments have been relied on by generations of Protestants, Catholics, Mormons, and Jews, and to try to remove them for Muslims both is unjust to Muslims and sets a dangerous precedent for other religious groups.

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Before Christian and Jewish believers support such measures, they should consider the way these laws not only misunderstand the faith of their Muslim fellow citizens but threaten their own religious liberty. Muslim Americans who seek to use Sharia are not asking the American legal system to adopt Islamic rules of conduct, penal or otherwise. Muslims have introduced Sharia in court not in an attempt to establish a freestanding source of law binding on litigants but rather in recognition of the norms to which the litigants have already agreed to be bound.

American courts do this every day—it’s called contract law. Even the literature being pumped out by anti-Sharia organizations shows that their target is not the threat posed by the imposition of Sharia on American society but rather the threat posed by the introduction of Sharia according to the same criteria of admissibility applied by courts to other religious codes.

Vischer gives an example of a Baptist church, whose rules may state that a pastor can be removed only by a vote of the entire membership. If the court determines that a small group of members ousted the pastor without the required vote, the court will uphold the pastor’s challenge despite the fact that the rules are based on a religious commitment (i.e., the Baptist commitment to the priesthood of all believers).

Another example is when courts enforce arbitration agreements based on biblical principles pursuant to widely invoked rules of “Christian conciliation.” To exclude similar agreements between Muslims that are based on Islamic principles would be to violate their freedom of religion — and set a precedent that could jeopardize the religious liberty of Christians.

As Vischer adds, “the presumption that the deepest core values and convictions of religious Americans threaten the legal order by virtue of their source, without reference to their substance.” If we don’t want biblical principles to be terms excluded from American court system, then we can’t let Sharia be excluded either.

Joe Carter is an editor for The Gospel Coalition and the co-author of How to Argue Like Jesus: Learning Persuasion from History’s Greatest Communicator.