Many people today think that the terms "liberal" and "conservative" are empty terms. I think that's because they don't understand what the terms mean. They don't mean "Democrat" and "Republican." There are very liberal Republicans and very conservative Democrats. They don't mean that you believe a certain amount of what has typically been considered liberal (e.g., pro-environment, anti-poverty) or conservative (e.g., pro-life, anti-homosexual agenda) causes. Americans are such ideological muts theses days that one cannot judge another person's interpretive authority simply based upon what side of a particular issue he comes down on. What they do mean, however, has great relevance for us, and will also help us understand that, although liberals are free to believe whatever spirituality they wish, they cannot be genuine Christians.
But let's define the terms first. The term "liberal" really refers to a person whose primary interpretive authority of reality is the Self. The term refers to the liberal, or free, position one wishes to have in interpreting life and experience. He or she is free from external authority as the primary guide in interpreting life.
By contrast, the term "conservative" refers to someone who seeks to "conserve" an external authority (a religious book, a religious body, a tradition within culture). He or she has one or more external authorities that serve as a guide in interpreting reality. The primary authority, then, is external, outside the self, and cannot be altered by the Self, as the self is but a lesser interpretive authority that must give way to that higher interpretive authority.
The question then becomes, Can both of these maintain their essential identities and accept genuine Christianity at the same time? In other words, can one simply adopt Christianity within either grid? My answer is, No, and here's why.
Christianity, at its very core, calls everyone to a denial of the self. But the self cannot be placed in submission under Christ if in fact it must remain to interpret Christ and all that God has said and made in the first place. If self experience is the ultimate guide to life, then it cannot be denied. In essence, if one argues that Christ uses the self to disclose the true nature of reality, then the Self is the most important authority in all the world, as it is the means through which God/Christ comes to us. I must, therefore, exalt it, not deny it.
The problem with this, of course, is that if Christianity, at its core, is the denial of the Self, then it cannot be the exaltation of the Self. In other words, liberalism in its essence is the antithesis of Christianity in its essence, and unlike other theses and antitheses, these two are diametrically opposed and cannot be reconciled, being an absolute contradiction.
Please understand that I am not saying that I don't like liberals and therefore want to exclude them from my group. My point is that by the very definition and the very practical outworking of liberalism, it simply cannot be wed to Christianity.
What happens instead is that liberals, like so many other cultures do with secondary religions, syncretize their secular humanism (which is what an exaltation of the Self to the primary interpretive authority of life is) with Christian themes and language, but have to throw out its core in an effort to maintain the identity of being "Christian." But this is no more Christian than any cult that uses certain themes and language of Christianity to clothe itself, only to deny the very foundations and matrix of Christianity itself. The liberal cannot bow the Self to Christ because he is always and at all times bowing Christ to the Self.
A Roman convert in the early Church could have argued that Christianity is compatible with Caesar worship, and made Christianity about a generic sense of love and morality; but at its core, Christianity is a rejection of all other lords in the exaltation of the one Lord, Jesus Christ. Hence, one cannot serve two masters.
This is not a problem for a conservative matrix, since conservatism by definition places its interpretive authority outside the Self. This means one must simply come to the correct external authority God uses to disclose Himself, and of course, in Christianity itself, and I would argue also at its core, this is the Bible and the Church, or I should say, this is the Bible through the Church.
It's not that self is not present. It's just learning to take a backseat to Christ as He communicates the correct interpretation of reality through an external source and an external means first. And this is not what liberalism is capable of doing, lest it no longer be liberalism, i.e., a freedom from external authorities as primary interpreters of reality.
So liberals really can't be Christians, simply because a circle can't be a square. I know that sounds very narrow minded and mean to exclude a poor square that wants to be called a circle, but those are just the facts. I can redefine things to fit, but that's simply a rearrangement of words to make everyone feel better. It doesn't shift reality. I can use my oft cited example of claiming to be a butterfly, as long as I define "butterfly" to mean everything that defines a human and nothing that defines a butterfly. In the same sense, I can call liberals Christians as long as what I mean by Christian is everything that isn't Christian and everything that is secular humanism instead (again, by "secular humanism" I don't mean non-religious or non-spiritual).
The truth is there is no such thing as a conservative Christian either, since all Christians by definition must have their interpretive authority outside of the Self, as the Self is being humbled and denied that authority to dictate the true nature of reality. Hence, there are only Christians who are conservatives. There is simply no other category within Christianity.
I'm sure someone will simply say that this is just another case of mean old Christianity excluding another group, but such a person didn't bother to read what I wrote above with any sense of the point being made. My point is that liberalism and Christianity exclude one another. They reject one another. Liberals may like certain themes in the Bible, certain traditions, certain language, even certain doctrines; but they cannot allow the Bible and the Church to reside over them in interpreting life for them in an absolute sense. They simply cannot bow the Self down to another, as in their religion, the heart knows best (there's the assumption of that liberal anthropology again).
So when I speak of liberals, this is what I mean by it. I mean those who place themselves and their experiences as the primary interpreters of reality. External authorities are subjected to the Self rather than vice versa.
You can see why it makes no sense to continue the facade any longer. And you can also see why liberalism kills churches (Why bother going to church if the Bible it preaches or the truth in which it fellowships is inferior to what you can gather for yourself through meaningful experiences elsewhere?).
Unfortunately, what is said above will not gain much traction among liberals, and they will continue to claim to be Christians anyway, as do Mormons, as do Jehovah's Witnesses, etc. That's because very few people who have come to see Christianity as something to do with God really want to reject Christ outright. They would rather just reinvent Him in their own image, i.e., in the image they personally see as most worthy of their respect. So the claim, no matter how delusional and contradictory it may be, will continue; and we will continue to hear the term "conservative Christian" as one category of Christian, even though that is the only category within Christianity that can logically exist.