This World War I memorial in Bladensburg, Md., is at the center of a case before the Supreme Court. (Mark Gail/FOR THE WASHINGTON POST)

In an establishment-clause dissent five years ago, Supreme Court Justice Elena Kagan reminded the nation of its “norm of religious equality.” As she described it, that principle entailed “the breathtakingly generous constitutional idea that our public institutions belong no less to the Buddhist or Hindu than to the Methodist or Episcopalian.” Now, the ideal of religious equality is facing a critical test.

On Wednesday, the Supreme Court will hear arguments on whether a 40-foot Latin cross may be displayed on a traffic island in Bladensburg, Md. Remarkably, most observers believe that the court will uphold the town’s right to display the Christian symbol. They understand that we are living through a historical moment when the Roberts court is fundamentally reworking the establishment clause, which guarantees the separation of church and state.

The court is increasingly upholding government support for religion that is neutral in theory, even if it favors the majority religion in practice. Yet we hope that the other justices will join Kagan and safeguard the principle of religious equality. Today, it is essential to voice the ideal of free and equal citizenship for all Americans — if only in another dissent written for a future when historical conditions again permit an egalitarian establishment clause.

In that previous case, the town of Greece, in Upstate New York, opened its legislative sessions with a prayer that was invariably offered by Christian clergy and that was predominantly Christian in content. The court upheld the practice anyway, because the prayers were open to all, in theory. The town had an (unpublished) policy that anyone could offer an invocation. Though the prayers were sectarian — referencing specifically Christian beliefs — they were excused by the town’s formally neutral policy, according to the Roberts court. Kagan dissented in an opinion joined by Justices Ruth Bader Ginsburg, Stephen G. Breyer and Sonia Sotomayor. That the prayers were exclusively Christian in practice violated the principle of civic equality, she noted.

Kagan explained that Americans do not stand before their government as adherents to one religion or another but as citizens. People in this country “participate in the business of government not as Christians, Jews, Muslims (and more), but only as Americans — none of them different from any other for that civic purpose.” According to the “First Amendment’s promise,” she said, “every citizen, irrespective of her religion, owns an equal share in her government.” When a majority religion is promoted through official speech or action, by contrast, the legal relationship between citizens and their democracy is transformed. We would add that government religiosity not only divides citizens but also stratifies them, relegating minority adherents to a subordinate status.

Kagan asked us to imagine a Muslim citizen who comes before the town legislature to express a policy perspective or request a permit. Just before she does so, a minister deputized by the town offers a prayer “in the name of God’s only son, Jesus Christ” (words uttered in one actual invocation). That citizen will reasonably conclude that the town’s governance is intertwined with Christianity and that she is excluded. “At the least,” Kagan explained, “she becomes a different kind of citizen, one who will not join in the religious practice that the Town Board has chosen as reflecting its own and the community’s most cherished beliefs. And she thus stands at a remove, based solely on religion, from her fellow citizens and her elected representatives.”

The Bladensburg cross creates the same sort of differentiation among citizens, stratifying them on the basis of religion. The cross was conceived in the 1920s to memorialize veterans of World War I, and it was located on public land. In 1922, the government conveyed the parcel to the American Legion for the purpose of completing the cross. But in 1961, the government then reacquired the land to maintain the monument, which had become unsafe. It has owned the land and the cross ever since.

Though technically the cross belongs to a larger park that includes secular war memorials, in practice the Bladensburg cross is singular, standing alone in the middle of a busy intersection, whereas the other monuments cannot easily be seen by passing motorists. And it dwarfs any surrounding symbols in sheer size. Jews or Muslims who drive by the monumental cross at the center of town will reasonably conclude that Bladensburg has a special relationship with its Christian citizens, one from which they are excluded.

The Latin cross is sectarian, just as the legislative prayers were: It is the central symbol of a particular religion and not others. While the government argues that the cross is serving the secular purpose of honoring veterans of Prince George’s County, in fact the cross carries “deep meaning, subscribed to by many, denied by some,” as Kagan put the point in the prayer case. It therefore differs from ecumenical references to God that solemnize government documents and ceremonies, such as the phrase “under God” in the Pledge of Allegiance or the national motto “In God we trust.”

Saying that the cross is merely ceremonial, and downplaying or even denying its religious significance, must be offensive to many Christians. What Kagan said of prayer in the name of Jesus Christ is true of the Latin cross as well: If it “ever become[s] mere ceremony, this country will be a fundamentally different — and, I think, poorer — place to live.”

It cannot be said that the cross is not a big deal — because of its age, or because it commemorates fallen soldiers, or because it was erected by a private organization. As the dissenters wrote of the legislative prayer in Town of Greece v. Galloway, it “is a big deal, to Christians and non-Christians alike,” and consequently it carries the power to differentiate and denigrate citizens. Like those justices, we would acknowledge the depth and diversity of Americans’ religious commitments “along with the challenge they can pose to the project — the distinctively American project — of creating one from the many, and governing all as united.”

Before the Roberts court, that project of religious neutrality was more widely shared, if not universal. For example, the Rehnquist court struck down a town’s holiday display that featured a Christian creche. It adopted the approach of Justice Sandra Day O’Connor, a Republican appointee, and it affirmed that the establishment clause, “at the very least, prohibits government from appearing to take a position on questions of religious belief or from making adherence to a religion relevant in any way to a person’s standing in the political community.”

We hope that on Wednesday the justices once more will voice their commitment to free and equal citizenship for all Americans. Ideally, the majority would embrace Kagan’s view — and O’Connor’s. But given the composition of the court, the principle of religious equality may well remain a dissenting position. It is necessary to preserve that commitment nonetheless, not only for a future time when judicial circumstances are different but also to guide Americans outside the courts who are reflecting on what they owe one another, engaged as they are in the cooperative project of democracy.