This question may be more complicated than it first appears, for the answer depends entirely on what one means by “a Christian nation.” Wayne Grudem does an excellent job of breaking this question down into nine possible interpretations, along with their respective answers, in his book Politics According to the Bible.
As Grudem explains, this question cannot be answered with a simple “yes” or “no.” Unfortunately, heated debate and frustration have often surrounded this issue. But the matter can be largely resolved if we simply take the time to define what we mean. This helps avoid misunderstanding and prevents disagreeing parties from talking past one another.
So is America a Christian nation? Let’s look at nine possible meanings of that question along with their specific answers.
1. Is Christian teaching the primary religious system that influenced the founding of the United States?
Yes, it is. See this article by David Barton: The Founding Fathers on Jesus, Christianity and the Bible.
2. Were the majority of the Founding Fathers of the United States Christians who generally believed in the truth of the Bible?
Yes, they were. See this article by Greg Koukl: The Faith of Our Fathers.
3. Is Christianity (of various sorts) the largest religion in the United States?
Yes, it is.
4. Did Christian beliefs provide the intellectual background that led to many of the cultural values still held by Americans today?
Here Grudem explains what he means by cultural values: “these would include things such as respect for the individual, protection of individual rights, respect for personal freedom, the value of hard work, the need for a strong national defense, the need to show care for the poor and weak, the value of generosity, the value of giving aid to other nations, and respect for the rule of law.”
The grounding for many of these cultural values can be found in the Declaration of Independence itself:
We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable rights, that among these are life, liberty and the pursuit of happiness.
In other words, if all men are created equal and are endowed by their Creator with certain unalienable rights, then it would seem that many things like respect for the individual, protection of individual rights, respect for personal freedom, etc., would naturally follow. The Biblical concept of the imago Dei, human beings created in the image of God, provides the appropriate grounding for many cultural values (such as human equality) that secularists often take for granted and which their own worldview cannot account for.
Answer: Yes, it did.
5. Was there a Supreme Court decision at one time that affirmed that the United States is a Christian nation?
Yes, there was. In 1892 the United States Supreme Court determined, in the case of The Church of the Holy Trinity v. the United States, that “this is a Christian nation.” After surveying the historical evidence of Christian founding and influence in this country, Associate Justice David J. Brewer concluded the following:
There is no dissonance in these declarations. There is a universal language pervading them all, having one meaning; they affirm and reaffirm that this is a religious nation. These are not individual sayings, declarations of private persons: they are organic utterances; they speak the voice of the entire people.
If we pass beyond these matters to a view of American life as expressed by its laws, its business, its customs and its society, we find everywhere a clear recognition of the same truth. Among other matters note the following: The form of oath universally prevailing, concluding with an appeal to the Almighty; the custom of opening sessions of all deliberative bodies and most conventions with prayer; the prefatory words of all wills, “In the name of God, amen”; the laws respecting the observance of the Sabbath, with the general cessation of all secular business, and the closing of courts, legislatures, and other similar public assemblies on that day; the churches and church organizations which abound in every city, town and hamlet; the multitude of charitable organizations existing everywhere under Christian auspices; the gigantic missionary associations, with general support, and aiming to establish Christian missions in every quarter of the globe. These, and many other matters which might be noticed, add a volume of unofficial declarations to the mass of organic utterances that this is a Christian nation.
6. Are a majority of people in the United States Bible-believing, evangelical, born-again Christians?
Here Grudem answers, “No, I do not think they are.” I agree. For support Grudem cites a 2005 Gallup poll which concluded that only 22% of Americans hold to truly evangelical beliefs. Even if Roman Catholics are grouped together with evangelicals, it still does not constitute a majority.
7. Is belief in Christian values the dominant perspective promoted by the United States government, the media, and universities in the United States today?
No, it is not.
8. Does the United States government promote Christianity as the national religion?
No, it does not.
9. Does a person have to profess Christian faith in order to become a US citizen or to have equal rights under the law in the United States?
No, certainly not.
To summarize, with these nine possible interpretations (and perhaps more!) in mind, it seems the appropriate follow-up question to “Is America a Christian nation?” is “What do you mean by that?” Grudem answers the first five questions above “yes” and the last four questions “no.” He concludes:
I do not think the question is very helpful in current political conversations. It just leads to arguments, misunderstanding, and confusion. The same points that a speaker wants to make with this claim can be made more clearly, without causing confusion, in terms of one or more of the expanded meanings that I have listed above.
Check out Politics According to the Bible for helpful insight on political issues from a Biblical perspective.
 Wayne Grudem, Politics According to the Bible: A Comprehensive Resource for Understanding Modern Political Issues in Light of Scripture (Grand Rapids: Zondervan, 2010), 64-65.
 Ibid., 64.
 Church of the Holy Trinity v. United States. Argued and submitted January 7, 1892. Decided February 29, 1892. Justice Brewer delivered the opinion of the court, as quoted in Gary DeMar, America’s Christian History: The Untold Story (Powder Springs, GA: American Vision, 2008) 10-11 (my italics).
 Grudem, Politics According to the Bible, 65.