What a debt the English language owes to George Orwell's Nineteen Eighty-Four. So many of its words and phrases have become common currency in everyday language: 'Big Brother is watching you', 'doublethink,' 'Room 101', to cite just three examples.

Among them all however one in particular stands out for me. 'Thoughtcrime' is the idea that the holding of a thought or a belief, without even expressing it, can in itself be a crime.

I've long recommended regular reading of Nineteen Eighty-Four. After a year in which in a new orthodoxy around issues such as nationalism and migration seems to be ever more prevalent, that advice is particularly salient. It seems to me to be more important than ever to promote the right to think for oneself.

To take this one stage further: it's more important than ever, in an apparently 'post-truth' culture, to promote thinking itself, as a good in its own right. As journalist Jonathan Freedland commented on the 'post-truth' phenomenon: "Evidence, facts and reason are the building blocks of civilisation. Without them we plunge into darkness."

In words that have been much shared on social media recently, Dietrich Bonhoeffer wrote this: "Against stupidity we are defenceless... reasons fall on deaf ears, facts that contradict one's prejudgment simply need not be believed... and when facts are irrefutable they are simply pushed aside as inconsequential, as incidental" (Letters and Papers from Prison).

It amazes me that such things have to restated, but in a world in which 'experts' are all too readily dismissed (including the vast majority of climate change scientists), that is what we have to do. The right to think for oneself, and the necessity of thinking, are non-negotiable and accusations of 'thoughtcrime' must be resisted at all costs.

So far so good. But what has all that got to do with Christian mission and is there anything particularly special about religious freedom – the freedom of specifically religious thought and expression?

Article 18 of the Universal Declaration of Human Rights makes no particular distinction. It says: "Everyone has the right to freedom of thought, conscience and religion; this right includes freedom to change his religion or belief, and freedom, either alone or in community with others and in public or private, to manifest his religion or belief in teaching, practice, worship and observance."

As the leader of a Christian mission agency that serves in a vast variety of cultures, countries and contexts, some of which try to restrict religious liberty, it seems to me absolutely right not to differentiate between religious freedom and any other kind of liberty of thought. Special pleading seems quite out of place. We must not claim for ourselves something we might deny to others.

Christian mission, in fact, depends upon freedom of thought and on the ability to think. True, the decision to follow Christ is much more than a matter of the mind, but it is certainly not less than that.

Of course the history of Christian mission has been littered with stories of forced conversion and heresy trials were horrible examples of 'thoughtcrime', but it should not be like that. We do not seek coercion, we claim freedom for other people to discover Jesus in their own cultural context, and having found him, to enter into "the glorious freedom of the children of God".

One of our people in mission in North Africa recently told us of a woman in Libya who had a dream in which Jesus appeared to her. Fortunately, a missionary was at the right place at the right time to gently answer her questions about this "imam in white".

We live in a world which constantly tries to tell us what to think and whic so bombards us with data that rational reflection becomes nearly impossible. But social media doesn't open us up to debate, it locks us down into a self-referential group within which our own prejudices are confirmed. Advertisers bombard us incessantly with a particular market-driven, consumerist world-view.

Against that we have to stand up with a loud insistence that we will think for ourselves, and think and believe whatever we choose to think and believe. We will avail ourselves of the freedom we have within our own minds to question the world around us, as well as ourselves, and that freedom will not be denied to us.

And in the openness and freedom of that thought, as Christians, we will welcome in the One who tells us that He has come to make us free indeed. And we will pray and work and persuade that others too, in the freedom of their own thought, will find the liberty that Jesus Christ alone can bring.

Rev Canon Philip Mounstephen is executive leader of the Church Mission Society.