In John 14:6, Jesus famously utters "No one comes to the Father except through me." This verse, I believe, is often misinterpreted. Christians tend to substitute a narrow, normative human lesson in place of the larger spiritual truth.
The "small" interpretation of this verse is this: only Christians are saved, and perhaps, as a corollary, God only listens to the prayers of Christians.
Now at a certain level this is an indisputable conclusion of what Jesus plainly says: No one has access to the father, with the implication being that the Father is favorably disposed toward no man, except and unless Christ intervenes.
We must, however, be careful about how we define "Christian." For practical purposes we define it in the normative sense: one who makes a credible profession of faith, and then follows that up with a life that bears fruit. All such people we are to judge as Christians. And others, which would include some who claim the title, (e.g. Fred Phelps) we are to judge as non-Christians (c.f. Matt. 7.)
This definition is imperfect, we all would admit. However, it is the only one available to us, and the bible instructs us to use it—but we must acknowledge that it will result in both false positives and false negatives.
This imperfect definition of Christian cannot be what our perfect Lord is talking about in John 14:6. He cannot be saying: nobody comes to the Father except those who make a credible profession and who appear to bear fruit.
No, Jesus is dealing with a set of people about whom there is no ambiguity. There is a precise set of people who have access (in the favorable sense) to the Father, and each and every one of them has access by the Son.
Who are these people? In general there would, all scripture seems to indicate, be a considerable though imperfect overlap with the visible church.
But in reality, this group of people is not limited to those with credible professions of faith who appear to bear fruit, but rather to those who are made presentable before God by the righteousness of Christ. All such people are Christians, and all Christians are such people.
Making a credible profession and bearing fruit is surely recommended. Without it you can have no confidence. However, it is neither necessary (though it is normative) nor sufficient.
What you must do to have the access to the Father described in John 14:6 is to be clothed in the righteousness of Christ. And we have but a limited, imperfect way in which we are to judge those who meet this requirement, and as such we cannot put God in a box.
The great truth of Calvinism is that God has mercy upon whom it pleases God to have mercy. This is readily accepted in the case of dead infants, where even the stoutest Arminian becomes a dogmatic Calvinist. (Well, to be fair, some avoid Calvinism by invoking a non-existent age-of-accountability with which to transport all dead babies to heaven, without pondering that such a doctrine transforms abortion from murder to mercy killing.)
I brought this up because I have been reading a few posts about whether theistic evolutionists can be Christians and whether or not evolution is compatible with Christianity. For example, here is one.
I hope the preceding discussion will help make clear the answer I am about to give:
Of course one can believe in evolution and be a Christian.
And of course evolution is "compatible" with Christianity. If it is true, then obviously so. If it is not, then it still is because Christianity makes no demand that we get all things right. Again, I am speaking in the absolute sense: he for whom Christ intercedes, he is a Christian, period.
Favorable access to the Father, through the Son, is the precise definition of Christianity. The single defining doctrine of Christianity is not he who believes the right things is a Christian (certainly a good sign) but he who is justified by Christ's righteousness, which is made manifest in faith, is a Christian. This is the absolute, bullet-proof sense.
That is truly the definitive doctrine of Christianity: if you approach God with Christ's righteousness you will be justified, regardless of your theology, and if you approach God with your own righteousness, you'll be cast out regardless of your theology.
There is no doctrine of justification by saying the right things. There is no doctrine of justification by behaving the right way. There is no doctrine of justification by having the correct view of the beginning times, middle times, or end times. There is not even a doctrine of justification by having the correct doctrine of justification.
Of course people who believe in evolution can be Christians. Of course YECs and OECs can be Christians. Or are you prepared to tell God: no, trust me, that person cannot be justified, even through the intervention of your Son, don't even try, it's no use.
The problem, of course, is that we have no way of seeing this absolute definition of a Christian. We are stuck with the normative definition: if you say and especially do, more or less, that which is expected. For me saying the right thing has always meant affirming the historic creeds. My litmus test is this: anyone who affirms the Nicene creed and who behaves, in some vague sense, like a Christian--him I will accept as a Christian. That makes my circle pretty big--but then again I'm one of those optimistic, starry-eyed postmillennials.