In a context of confusion and flashy journalism, rigour becomes a precious value.
It is one thing is to work together on areas of common concern in society, e.g. the promotion of Judeo-Christian values in society; it is an altogether different issue to engage in common mission and evangelism.
In our global world, a cluster of questions are before evangelicals: Should we collaborate with Catholics? On which topics or areas? How far should we go? Is it possible to do mission together?
Of course, much depends on the various contexts and those who are involved. For example, is it one thing to work with individual Catholics or lay groups; it is something else to join hands with the institutional Church of Rome. It is one thing is to work together on areas of common concern in society, e.g. the promotion of Judeo-Christian values in society; it is an altogether different issue to engage in common mission and evangelism.
Alliance and Co-belligerence
To start unpacking the issues involved, it may be useful to remember the lesson of 20th century Evangelical apologist Francis Schaeffer (1912-1984). Schaeffer was a Christian leader who introduced the expression co-belligerence to the present-day Christian vocabulary. In the midst of the cultural transitions of the Seventies, he encouraged Evangelicals to side with people of other religious persuasions for the sake of promoting specific issues that were shared by a cross-section of society and that were under threat by secular tendencies, especially in the realm of basic moral values. Schaeffer’s call to engage in the public square, working together with non-Christians, has been one of the motivating factors of recent Evangelical involvement in society.
In suggesting a rationale for co-belligerence, Schaeffer made a distinction between forming alliances and engaging in co-belligerence. On the one hand, an alliance is a kind of unity based on truth, and therefore has to do with born-again Christians only who receive Scripture as the standard of their lives. On the other, co-belligerence focuses on a specific issue and is open to all those who share it, whatever their backgrounds and the goals that motivate them. Here is how Schaffer defines it: “Co-belligerent is a person with whom I do not agree on all sorts of vital issues, but who, for whatever reasons of their own, is on the same side in a fight for some specific issue of public justice”. For Schaeffer this distinction reflects Scriptural principles about unity among believers and cooperation among people of different faiths. Co-belligerence is not another way of talking about ecumenism. The latter has to do with unity of believers according to the Bible; the former is related to possible cooperative efforts among different people and beyond agreement on central truths of the Gospel.
The distinction between alliance and co-belligerence reflects the teaching of Scripture. Unity exists deep within the people of God on the basis of a common faith in Jesus Christ (Ephesians 4:1-16). This unity allows alliances in terms of worship, prayer, evangelism and Gospel witness. This unity allows the church to work out the Great Commission that Jesus gave to go all over the world and disciple the nations (Matthew 28:16-20). This type of alliance shows the power of the Gospel to reconcile different people around the same Lord Jesus who sends His people forth to take the message of reconciliation to the world (2 Corinthians 5:17-20). This unity is not what co-belligerence is all about.
The Scripture clearly distinguishes the unity of believers in Christ from other types of relationships without separating them. The Bible commands all men and women (Christians included) to inhabit the earth responsibly, taking care of the world and living peacefully as much as possible. Then, the Word of God encourages the church to develop and maintain good relationships with their neighbours and to be committed to the good of others (Genesis 1:27-31; Jeremiah 29:5-7; Titus 3:1-2). In doing what the Bible requires, we will be always in contact with different people who hold a plurality of worldviews and lifestyles. Our family members, co-workers, roommates, and friends may not be believers, yet we are called to live with them for the good of the community.
In this sense, co-belligerence is necessary, useful and ... inevitable. It is a task of our God-given humanity. It is part of our common calling to live in this world without being of the world (John 17:14-18). For the Christian, neither total retreat nor self-imposed exclusion from the world is a viable option. The Christian life requires one to develop and nurture multiple networks of social relations. A mature faith is able to maintain different relationships with different people, without losing its Christian identity and Gospel commitments. The important thing is to practice the distinction between alliance and co-belligerence.
Alliance or Co-belligerence?
Back to the question we asked at the beginning. As far as our relationship with the Roman Catholic Church, should evangelicals engage in alliances or acts of co-belligerence? Schaeffer encouraged co-belligerence with people of all persuasions, but would limit alliances to Bible-believing, born again Christians, therefore excluding the Church of Rome as an institution. The basic issue to address is whether or not the Catholic gospel held by the Church of Rome is the biblical gospel in its basic contours. The answer to this question leads to answering the previous one. If the answer is “yes”, i.e. the Roman Catholic gospel is the biblical gospel, then it follows that no theological restriction needs to be put in place. If the answer is “no”, i.e. the Roman Catholic gospel is not the biblical gospel in significant ways, then there needs to be a careful discernment not to blur the distinction between collaborating on social issues and engaging in common mission. The former is possible, the latter isn’t.
 Plan for Action (Old Tappan, NJ: Flemming H. Revell, 1980, p. 68). Schaeffer spoke about co-belligerence in the second chapter of his book The Church at the End of the Twentieth Century (1970) various editions.