The Verification Principle

First, I will discuss a group of philosophers and scientists, known as the Vienna Circle. They met throughout the 1920s and into the '30s to examine subjects including logic, language and meaning.
The thinkers were influenced by Ludwig Wittgenstein, who believed that we can only use language to explore natural scientific propositions and trying to talk about the metaphysical, or that beyond our world, is impossible. They belonged to a movement called Logical Positivism, which maintains that language and conversation is only meaningful if it can be verified (i.e. proved to be true) empirically. Therefore, all religious language, or "God-talk", is meaningless because it does not relate to a reality that can be verified by a posteriori reasoning.
For a logical positivist, claims such as:

-"God is love"
-"The soul is non-physical" 

are completely meaningless because there is no observation or experience that could demonstrate the sentences are true or false, and whether they are true or not makes no difference to our experience. As these statements are not confined within the limits of human experience, therefore they are nonsense.

The most notable principle that is associated to logical positivism is The Verification Principle, which was famously argued by A.J. Ayer in his book, "Language, Truth and Logic".

All statements can be categorized as either:
1) Analytic (i.e. a statement is true by definition) - it is a tautology and the wording of the statement verifies the truth of it.
2) Synthetic (i.e. a statement can be verified through empirical evidence) - it is meaningful and factually significant because they can hold verifiable truths.

Therefore, the Verification Principle states that if a statement is neither true a priori, nor empirically verifiable, it says nothing about reality and therefore is meaningless. This can be used to identify claims that appear to tell us something about the world we live in, but really if it's truth cannot be known then it is not worth discussing. An example comes from John Hick, "The universe doubled in size last night", which illustrates how a statement can appear to attempt to tell us something about our world at first, but after deeper analysis, it is revealed that a claim like this does not truly say anything about what the world is like.

What are the implications for religion?

As God is a transcendent being, completely beyond human understanding, all conversations about God will fail because humans do not have an adequate understanding of his nature. For Ayer, no matter whether a person has a perspective of theism, atheism or agnosticism, any "God-talk" is meaningless because there is no empirical verification of religious propositions. He would reject religious concepts such as life after death, and the belief in a non-material soul, simply because they are not verifiable. Religious language related claims are subjective (i.e. they are not factually significant) and therefore, they cannot be practically verified (i.e. conclusively verified using empirical evidence), or even verified in principle (i.e. shown to be highly probably by observation). However, the fact that the verification principle allows this loophole for scientific propositions - which often can only show that they are the most probable explanation, rather than conclusively prove they are right - greatly weakens, because many claims could be verifiable 'in principle'.
Hick would argue that all religious propositions will be verified eschatologically, and therefore they can be considered to be factually significant and meaningful. This suggests a distinctly different understanding of 'verification' to Ayer's, and indeed, for Hick something can be verified if it is possible to remove reasonable doubt of the truth of the claim. As it is possible that God exists and there is the possibility of an eternal life in heaven, then all religious claims are potentially verifiable and meaningful. Therefore, for a Christian who believes in an after-life it is possible that all their beliefs will be verified after their death, and therefore conversations about their faith are truly meaningful.