On a host of doctrinal and practical concerns, the challenge often is to avoid the extreme either of confusing things that should be distinguished or separating things that should be held together.

A case in point is evangelism and social justice. Evangelicalism has long been divided over this question. Charles Finney, leader of the Second Great Awakening, called the church a "moral reform society," while a later generation would follow the pioneering remark of evangelist D. L. Moody, who compared the world to a sinking ship. We're only left here to save as many souls as we can, Moody argued.

And now the pendulum seems to be swinging in the other direction, away from Moody and back toward Finney. There are many things that could be said regarding the deeper theological issues, but my point in this brief space is to address the question of Roman Catholic and Reformed cooperation in the civil sphere, specifically related to mercy ministry.

First, it's important to note that the Reformed tradition has always affirmed God's concern for bodies as well as souls. In its doctrines of creation, the fall, redemption, and consummation, human beings are regarded as whole persons, not merely as minds or souls trapped in a body for a while. With Christians of all ages, we confess "the resurrection of the body and the life everlasting." This concern for temporal welfare is evident in the renewal of the diaconate in Calvin's Geneva. In Roman Catholic and most Lutheran churches at the time, the deacon was basically an "associate pastor." However, Calvin's study of Scripture led him to the conviction that the diaconate was a different office, with different gifts and goals. In a city swelling with refugees, the deacons and deaconesses were often former monks and nuns who oversaw and administered Christ's priestly work of service to the poor and suffering.

The more controversial question is whether the church as a divinely ordained institution is commissioned to establish mercy ministries for the world at large. Though not central, this point is germane to my argument, which should become clear below. Scripture clearly includes diaconal care of the saints in the mission of the church, but in my view it does not authorize the creation of agencies for general relief, cultural engagement, political causes, and similar important but nonecclesiastical operations.

We don't have to choose between Finney or Moody. The church is neither called nor competent to satisfy every human need, but that in no way eliminates the responsibility of Christians to love and serve their neighbors. Once we distinguish properly between the calling that Christ gave his church in the Great Commission from the calling he gives to all people in the Great Commandment, we can go some distance toward evaluating the case for Reformed-Roman Catholic cooperation.

The Great Commandment and the Great Commission

A young lawyer asked Jesus, "Teacher, which is the great commandment in the Law?" Jesus replied, "You shall love the Lord your God with all your heart and with all your soul and with all your mind. This is the great and first commandment. And a second is like it: You shall love your neighbor as yourself. On these two commandments depend all the Law and the Prophets" (Matt. 22:36-40). Jesus was simply repeating Moses (Lev. 19:18; Deut. 6:5). The second is like the first, not only because it summarizes the second table of the Law (love your neighbor), but also because love of God is inseparable from love of neighbor.

The moral law of God is written on the conscience of every human being. As such, it forms the core of every civil constitution (written or unwritten)—to the extent, at least, that it is not wholly suppressed in unrighteousness. This original, inner, universal, and intuitive word of God (general revelation) is different from that surprising, external, particular, and disorienting good news (special revelation) that has to be brought by a herald.

This general perception of moral law, as part of the common grace of God, establishes a temporary peace, order, justice, and civility in this present evil age. Because of it, Christians can work alongside non-Christians in their common vocations. Although non-Christians are using borrowed capital, there is no reason to assume that Christians will always be wiser, more tender and loving, or better-informed in worldly affairs than non-Christians. They should, but the sinful nature and the common grace that we all share tend to level the playing field.

So when it comes to loving our neighbor, from globalization and human rights to caring for an elderly parent, Christians can make common cause with adherents of other religions and even agnostics and atheists. Even the philosopher Immanuel Kant retained an infallible certainty of "the moral law within" after rejecting supernatural religion. Evangelical and Reformed Christians have found themselves cherishing the friendship and collaboration of non-Christians in service to the common good.

Nevertheless, the Great Commandment is not the Great Commission, and the law is not the gospel. Christians cannot choose between these mandates; they owe their allegiance to both, simultaneously, as God's redeemed creatures being renewed after Christ's image and also as ambassadors and heralds of Christ's kingdom of grace.

Reformed-Roman Catholic Cooperation?

At last, then, we come to the heart of the question I'm addressing in this article. On November 20, 2009, evangelical and Roman Catholic leaders released a common statement, "The Manhattan Declaration: A Call of Christian Conscience." Though dated somewhat now, the Declaration is the latest in a series of "Evangelicals and Catholics Together" initiatives. Drafted by Princeton professor Robert George and evangelical leaders Chuck Colson and Timothy George, this declaration focuses on three issues: (1) the inherent dignity and rights of each human life (including the unborn) by virtue of being created in God's image, (2) the integrity of marriage as a union of one man and one woman, and (3) religious liberty, also anchored in the image of God.

There is a lot of wisdom in this document. For one, it does not breathe the vitriol that is too common on the religious right and left. In this declaration, one will find more light than heat, and there is a sense of personal concern for the humaneness of the common culture, even for those who are pursuing antithetical agendas. May this more thoughtful approach to public engagement become more characteristic!

The authors wisely appeal to natural law as well as to Scripture and its revealed doctrines. After all, these three issues are grounded in creation. However, it is just for that reason that I stumbled over a few references to the gospel in this declaration. It took me back to the old days of "Evangelicals and Catholics Together," when I joined others in raising concerns that this 1996 document announced agreement on the gospel while recognizing remaining disagreement over justification, merit, and the like. Many true and wonderful things were affirmed in that ECT document, but the gospel without "justification through faith alone apart from works" is, as I said then, like chocolate chip cookies without the chips.

This later declaration continues this tendency to define the gospel as something other than the specific announcement of the forgiveness of sins and declaration of righteousness solely by Christ's merits. The document recites a host of Christian contributions to Western culture, adding, "Like those who have gone before us in the faith, Christians today are called to proclaim the Gospel of costly grace, to protect the intrinsic dignity of the human person and to stand for the common good. In being true to its own calling, the call to discipleship, the church through service to others can make a profound contribution to the public good." The declaration concludes, "It is our duty to proclaim the Gospel of our Lord and Savior Jesus Christ in its fullness, both in season and out of season. May God help us not to fail in that duty." In an interview, Colson repeatedly referred to this document as a defense of the gospel and the duty of defending these truths as our common proclamation of the gospel as Roman Catholics, Orthodox, and evangelicals.

Having participated in conversations with Colson on this issue, I can assure readers that this is not an oversight. He shares with the late Pope John Paul II and Pope Benedict XVI the conviction that defending the unborn is a form of proclaiming the gospel. Although these impressive figures point to general revelation, natural law, and creation in order to justify the inherent dignity of life, marriage, and liberty, they go too far when they make this interchangeable with the gospel.

The error at this point is not marginal. It goes to the heart of the more general confusion among Christians of every denominational stripe today, on the left and the right. The law is indeed the common property of all human beings, by virtue of their creation in God's image. As Paul says in Romans 1 and 2, unbelievers may suppress the truth in unrighteousness, but the fact that they know this revelation makes them accountable to God. However, in chapter 3, Paul explains that a different revelation of God's righteousness has appeared from heaven: God's justification of the ungodly through faith alone in Christ alone.

When we confuse the law and the gospel, there is inevitably a confusion of Christ and culture, and there is considerable evidence in Roman Catholic, Orthodox, and evangelical histories to demonstrate the real dangers of this confusion. In this otherwise helpful declaration, the confusion is evident once more. Alongside the theological claims that witness to the dignity of all people created in God's image, Christianity seems to be defended as a major stakeholder in Western culture and society. By tending to confuse the gospel with the law, special revelation with general revelation, and Christianity with Western civilization, the document actually undermines its own objective—namely, to defend the dignity of human life as a universal moral imperative. Both Christians and non-Christians are recipients of this general revelation.

The church has a responsibility to proclaim the gospel of free justification in Christ and to witness to God's universal rights over humanity in his law. We interpret both as Christians, but can appeal to the conscience of our fellow image-bearers with respect to the latter. The law is God's command, but it cannot save; it is not the gospel, which is alone "the power of God for salvation to everyone who believes" (Rom. 1:16).

So where does this leave us? If we must beware of confusing the law and the gospel, the Great Commandment and the Great Commission, we dare not separate them. Although the Great Commission is given to the church alone, the Great Commandment is the moral charter for the whole human race. Surely, if we can work alongside non-Christians, we can find areas of common cause with our Roman Catholic neighbors.

But does this go far enough? Perhaps not. As Calvin famously said, Scripture gives us not only special revelation but also the spectacles that correct our reading of general revelation. Much of the richest and wisest Christian understanding of social questions is the common inheritance of Roman Catholics and Protestants alike. In fact, in recent decades especially, Roman Catholics have often exhibited a more consistent social ethic than mainline or evangelical Protestants. Together with Catholics and the Orthodox, we affirm the ecumenical creeds. In an age like ours, this broad consensus offers a wide and well-lit hallway in which to mingle, exchanging gifts of mutual correction and admonition on a host of matters of Christian responsibility in the world.

Obviously, though, this cooperation cannot be regarded as belonging to the Great Commission. This is the serious problem with documents like the Manhattan Declaration. According to this statement and its authors' interpretations of it, the only justification for speaking together on social issues is our common agreement in the gospel. However, this hinders both the Great Commission and the Great Commandment. It hinders the former because we (Reformed Christians, at least) do not have agreement with Rome on the gospel, and in such declarations the gospel and Christ's mission to deliver it are confused with the law and our cultural activities. It hinders the latter because a (false) Christian consensus in the public sphere often binds Christian consciences beyond Scripture and gives our non-Christian neighbors the impression that the church is another political action committee vying for social power. We need to remember that the common basis for working with anyone is the moral law, which is God's binding claim on us all. And with so many shared convictions regarding the triune God, creation, Christ, and a final judgment, confessional Protestants have every reason to cooperate with Roman Catholics in the cultural sphere.

If Christians are free to work with non-Christians in pro-life clinics, hospice centers, homeless shelters, relief and redevelopment agencies, hospitals, human rights organizations, and countless cultural programs, then cooperation with Roman Catholics should be especially valued. We share centuries of collective wisdom on everything from just-war theory to human rights, as well as civic morality and a love for the arts, letters, and sciences. Dare I say, we have a lot to learn from the Roman Catholic tradition on many issues, and sometimes we both have taken too much pride in our particular cultural contributions.

It is only by confusing the church as an institution with the church as saints scattered into the world as salt and light that we can be pressed into the false choice between assuming ecclesiastical-evangelical unity with Rome and refusing to cooperate with Roman Catholics at all.

The author is professor of systematic theology and apologetics at Westminster Seminary California. New Horizons, October 2011.