It is sometimes argued that because religious beliefs and experiences contradict each other, they can't all be true. Whilst I'm sceptical that religions are 'basically all the same' I also believe that this criticism isn't as strong as proponents believe.
Let's take these four theses for our purposes of comparison:
a) Jesus Christ is the Son of God;
b) Muhammed is the final prophet;
c) the Buddha teaches the noble truth;
d) the Flying Spaghetti Monster is the source of all goodness.
Now on the face of it, it is impossible to reconcile these four theses. At most only one can be true. Yet this is only the case if these theses are certain sorts of claims, principally, that the theses are factual claims about states of affairs in the world. It is as if there is a spiritual equivalent of the periodic table, and the claim in each of the four theses is that a particular entity occupies position #1. The other entities, however wonderful, cannot occupy that position, they have to occupy other numbers. As the Highlander tagline had it, 'there can be only one'.
To take the religious language in this way, however, is in my view to fundamentally mistake the grammar of religious language. Accepting this way of understanding religious language is, in fact, a hallmark of what I call the humourless perspective (both atheist and theist).
Wittgenstein said (PI § 43) "For a large class of cases - though not for all - in which we employ the word 'meaning' it can be defined thus: the meaning of a word is its use in the language." In other words, to understand what each of those four theses means - and therefore whether there is a contradiction involved - we need to look at what is actually being done with the words.
Now it is perfectly possible to imagine a Buddhist, a Muslim and a Christian whose lives closely resemble each other in certain particular respects, for instance that in response to suffering a wrong (being cheated in a business transaction) they each choose to forgive. Each one explains their behaviour in terms of their religious commitments: the Christian says that forgiveness is of God, the Muslim says he must follow Allah the compassionate and merciful, the Buddhist says something about the importance of cultivating boundless compassion to all creatures.
The point being that in this case, the meaning of the language is identical across the different religious beliefs. There is no more contradiction involved than there is when a Frenchman uses the word 'vache' where an Englishman would use the word 'cow'. Although the surface grammar of the statements appear contradictory, the depth grammar is the same.
Should we find someone who was a genuine worshipper of the Flying Spaghetti Monster, who, as a result of their spiritual disciplines and learning, ends up behaving in the same way (practising forgiveness) then we can say that their language means the same thing. We can even say the same thing about an atheist, or about someone who said nothing more about their behaviour than 'this seemed the right way to behave'. In each of these cases it is the behaviour which is fundamental and which gives meaning to the language used to describe it.
Which means that contradictions between religions come at the level of behaviour, not of speech.
For it is also easy to imagine Christians, Muslims and Buddhists who use the same language as their brothers and sisters in the faiths, but whose behaviour is markedly different. In response to being cheated in business, each one may respond with violence of thought and action, or resort to legal and judicial processes and so on. In this instance it becomes clear that there is certainly a contradiction between the beliefs of the first group and of the second - but the contradiction isn't a logical one (which person belongs in position #1 of the spiritual periodic table), the contradiction is one of behaviour.
One can push this a little further and say: the holy in each faith recognise each other and resemble each other. To use Jesus' language "Not everyone who calls me 'Lord' shall enter the Kingdom... but those who do the will of my father who is in heaven."
The fundamental claim of faith is that there is a right way to live, independent of our own choices. There are some disagreements across the faiths about what that right way is, but the disagreements should not be assessed at the surface level of grammar, but at the depth level of forms of life. Once that is done, and greater clarity is obtained about the claims of each faith, we can more easily see where the real contradictions obtain. Then, and only then, the conversation can become interesting and important.