Buddhism, Hinduism, Islam, Judaism and Christianity each make different claims about God. Which, if any of them, is true? On superficial inspection two extremes may suggest themselves. One is to conclude that all religions are equally false and the other is to wonder if all religions are equally true. But both extremes are unsatisfactory.
The idea that all religions may be equally true seems to take a hint from Symmachus who wrote that, “Infinite religions befit an infinite God.” The different world religions, the proponent of this view might reason, are disparate in aspect and identical in essence: Buddha, Moses, Muhammad, Brahma and Christ are like different emissaries God has chosen or different masks which he has worn—perhaps each one appropriate to the cultural and historical context in which he met us.
But religious relativism, or “syncretism” as it is sometimes called, is logically incoherent. The great world religions make conflicting claims about God. God, meanwhile, is morally perfect and this means that he does not, indeed cannot, lie. And if he cannot lie he cannot reveal two mutually exclusive doctrines about himself—one of which, by the law of noncontradiction, must be false. Consider the doctrine of the Incarnation. Christianity claims God become incarnate in Jesus. Islam denies this. And since it is not possible that God did and did not become incarnate in Jesus, Christianity and Islam cannot both be true. And so on for any number of conflicting religious doctrines.
Is, then, the first idea correct? Given a set of claims which cannot all be true it does not necessarily follow that all are false. Indeed, as William Lane Craig has observed, if it did then atheism would also be false since atheism, too, belongs to a set of claims about God that cannot all be true. Consider the following set of claims,
Mr Ito is in Osaka.
Mr Ito is in Tokyo.
Mr Ito is in Nagasaki.
Clearly, it is impossible that all three are true—Mr Ito cannot be in three different cities at the same time. Just as clearly, it is possible that all three are false—Mr Ito may be in Kyoto. But it is also possible that one of them is true since Mr Ito may in fact be in Tokyo.
Religious pluralism, then, does not entail that all religions are false but it does present a challenge to the coherence of each one, including Christianity. And the challenge is to explain why, if there is a God who revealed himself to us, he would allow potential confusion about that revelation. I suggest that the way to meet this challenge is to first understand religious pluralism as a subtype of the problem of divine hiddenness.  I will therefore find it helpful to briefly consider the problem divine hiddenness before drawing out its relevance to religious pluralism.
Proponents of the objection from divine hiddenness argue that if God really existed his existence would be overwhelming or, at the very least, not open to dispute. They further note that some people seek and do not find God and claim that this is inconsistent with the idea that God is all loving and wishes to have a relationship with us. In general, they claim that the fact that it is possible to doubt the existence of God is evidence against the existence of God.
In reply, the theist suggests that the attainment of virtue involves facing a choice between good and evil and choosing to do good. A morally perfect God therefore has reason to create agents capable of such freedom. However, a problem arises if the naked countenance of God is overwhelming. For in that case, finite agents given the beatific vision of God ab ovo would never experience the temptation to do evil. One solution would be for God to create an antecedent world from which his countenance is hidden and then populate it with agents who begin life in a state of moral and spiritual ignorance. But a further problem will arise if certain knowledge of God (if, say, theistic poofs exist, or knowledge of God is as salient and constant as sensory perception or self-awareness) is also a threat to moral liberty. Theists claim that this is so. Imagine, by way of illustration, a young child who senses his mother’s watchful presence at the nursery door. The desire to please his mother and the lack of a feasible prospect of misbehaving with impunity will in that moment completely extinguish all temptation and so leave him without significant choice. God has therefore temporarily situated himself at an “epistemic distance” in order to vouchsafe his creatures the opportunity to attain various moral goods that would otherwise be unattainable.
With this in mind consider the following three premises,
P1. It is not possible that God would specially reveal himself in two or more mutually exclusive religions. (Because a morally perfect being cannot lie).
P2. It is not plausible that there should be unresolvable uncertainty about a special revelation of God. (Because if God chooses to specially reveal himself he has both the reason and the means to miraculously authenticate his special revelation).
P3. It is plausible that God would permit resolvable uncertainty about his special revelation. (Because religious pluralism is a subtype of divine hiddenness and divine hiddenness vouchsafes human moral freedom).
It follows from P3 that prima facie confusion due to religious pluralism does not prove that God has not revealed himself. It follows from P1 that if he has revealed himself specially it will be in only one of a group of mutually exclusive religions. And it follows from all three premises that whatever religion has, on balance, the strongest a priori plausibility, and the strongest historical evidence, is far more probably than not, and far more probably than any other, a true revelation of God. 
In short, my suggestion is that God may have good reason for allowing humanity to form false conceptions of him while, at the same time, providing a revelation by means of which it can form a correct one. But in that case it must be possible for a determined and conscientious inquirer to distinguish the true conception from the false. And so the solution to the problem of religious pluralism is, finally, the intuitive and obvious one: Providing arguments and evidence to show that Christianity is more plausibly true than any other religion.
And while I believe that such arguments are available, that is a subject for another post.
 For a detailed discussion of divine hiddenness and the high-order goods solution that has been proposed to address it, see here.