There are no atheists in foxholes, or so goes the adage. There are also no sectarians (unwarranted church dividers) in foxholes. Secondary theological differences seem not just a silly triviality but also a dangerous luxury when your very life is at stake. This is one reason there’s traditionally been ecumenism (broad Christian unity and cooperation) on foreign mission fields. If a major problem of the 16th – 19th centuries was a kingdom-impeding sectarianism, the problem in the 20th century has been in the other direction: false unity.
The Ecumenical Movement of the early 20th century, driven partly by the growing encroachments of cultural secularism, was championed by Nathan Söderblom, whose now well-worn coinage “doctrine divides but service unites” became its theme. The kind of unity the Movement sought was an organizational unity that depended on lowest-common denominator theological cooperation. That organization became the (in)famous World Council of Churches. In time this marginalization of doctrine wedded to the Leftist Social(ist) Gospel turned the WCC into a hotbed of pro-Marxist propaganda at the very time Marxist regimes were advancing in — and enslaving — the Third World.
The quest for Christian unity in the face of Satanic onslaught isn’t wrong. Amid his early kingdom-advancing exorcism ministry, Jesus declared to his disciples, “[H]e who is not against us is on our side” (Mk. 9:50). Christians on the right side of kingdom work needn’t be of our tribe to be doing the right work. It’s a pity our forebears often missed this point, and we’re paying a heavy price for it today.
The Thirty Years’ War in Europe (1618–1648), pitting Roman Catholics, Calvinists, and Lutherans against each other, all entangled in regional politics, resulted in 8 million deaths. An exhausted continent welcomed an end to the horror, the brokered Peace of Westphalia. This treaty, among other provisions, vested national rulers with the authority to establish the religion of their country. This led, in turn, to religious toleration, because nobody wanted a rerun of 1618–1648. It’s a textbook example of a treaty that solved problems while creating others: it ended the war and fostered religious liberty, but it marginalized Christianity and paved the way for modern secular nation-states. Today’s statism is partly the consequence of this treaty, for in treating religion ( = Christianity) as relatively unimportant and the state as very important, religion as a cultural force withered, while the state flourished. This was a terrible price to pay for peace, but it would never have happened had not there been the pervasive, dangerous church-state union, and even more, had Christians been able to live together peacefully in their own separate churches within a broadly Christian culture. Such a peaceful arrangement wasn’t even a consideration at the time and formally came about only with the nonsectarian founding of the United States.
Today radical secularism and neo-paganism threaten the very heart and soul of Christianity in the West. Stand publicly for Christian sexual standards and you could lose your business. Oppose same-sex “marriage” on social media and you might get de-platformed. Maintain Christian dating standards on your Christian college campus and you could lose your accreditation. The New Barbarians aren’t targeting only Protestants (or evangelicals or Roman Catholics or fundamentalists); their assault is nonsectarian — they’re targeting Bible-believing Christians. (Note: there can be no liberal or “progressive” Christians.) The impulse to unite for not only repelling the attack but also retaking lost cultural territory isn’t merely a necessity — it’s a biblical imperative. “I am a companion of all who fear You, [a]nd of those who keep Your precepts (Ps. 119:63). “There is one body and one Spirit, just as you were called in one hope of your calling; one Lord, one faith, one baptism; one God and Father of all, who is above all, and through all, and in you all” (Eph. 4:4–6).
Christians should stand shoulder-to-shoulder to repel this Satanic flood, but we mustn’t make the false ecumenical mistakes of the past. Doctrine is vital, but the doctrine at the heart of the Faith, summarized in the Apostles Creed, not denominational distinctives like baptism, church government, or sign gifts. There can be no compromise on doctrines without which the Faith couldn’t exist. 
Perhaps even more vital is the true ground motive of the Faith: a heart turned totally toward the Triune God and its willingness to smash all idolatries and all obstacles to Christ’s biblical kingdom being established in the earth. Christianity requires theology, but a heart given totally to God and his kingdom precedes theology.
Such orthodox Christians can stand boldly together, not uniting in a single church (worshipping in their own distinctive churches) yet uniting in the great social battles for Christian culture: religious and political and economic liberty, the dignity of human life, biblical sexuality, and the Lordship of Jesus Christ in all of life and society. We unite for a Christian society under the victorious banner of Jesus Christ our King. We need not agree on many things to agree on that.
 Jaroslav Pelikan, Christian Doctrine and Modern Culture (Since 1700) (Chicago and London: University of Chicago Press, 1989), 303.
 Ernst W. Lefever, The Irony of Virtue (Boulder, Colorado: Westview Press, 1998), 69–73.
 No author, “Westphalia, Peace of,” The Westminster Dictionary of Church History, Jerald C. Brauer, ed. (Philadelphia: Westminster Press, 1971), 862–863.
 Thomas Oden, The Rebirth of Orthodoxy (New York: HarperCollins, 2003), 55–68.
 Herman Dooyeweerd, In the Twilight of Western Thought (Ancaster, Ontario, Canada: Paideia Press, 2012), 101.