Yesterday, the Edinburgh International Book Festival began. I feel sure that many of you will have happy memories of sitting in a very warm marquee in the middle of Charlotte Square and listening to distinguished speakers. Festivals of this and of all kinds should be peaceful and reflective events, open to a variety of perspectives. The vicious and life-threatening assault on Salman Rushdie at the Chautauqua Institute on Friday has been rightly and unequivocally condemned by many people.

It seems likely, given what is known about the alleged attacker, that he was motivated by an extreme and distorted version of his religious beliefs. That has, predictably, led to widespread comment on social media that the world would be a better and safer place if there were no religious believers. Some of that comment is reasoned, some of it is a reminder that secularists can be surprisingly intolerant, uncharitable and prone to sweeping generalisations.

In the light of all this, today’s Gospel makes particularly difficult reading. It’s one of those moments in the New Testament when we seem to have direct access to Jesus’ emotions. He confronts us with some powerful and very challenging words:

“Do you think that I have come to bring peace to the earth? No, I tell you, but rather division!”

And Matthew’s Gospel has an even starker version of this saying:

"Do not think that I have come to bring peace to the earth; I have not come to bring peace, but a sword.”

A few years ago, Susan and I went to a brilliant talk at the Book Festival by the historian Sir David Cannadine, and it came to mind when I looked at today’s challenging and uncompromising Gospel, because Sir David referred to it in his lecture.

Professor Cannadine also quoted that verse from Matthew but went on to suggest that it is essential to hold it in dialogue with other sayings of Jesus, including his teaching about loving your enemy and about turning the other cheek. And as we think about today’s Gospel, it is important to remember something that Jesus says a little earlier in Chapter 12 of Luke:

"Do not be afraid, little flock, for it is your Father's good pleasure to give you the kingdom.”

We value family life, delighting in its closeness if we are privileged to enjoy it and mourning deeply when family ties are broken by death, yet here is Jesus saying that his mission – the inauguration of the Kingdom of God - will divide families, setting close relatives against each other. On the face of it, this seems to add weight to the Humanist view of that religion is a bad thing precisely because it causes divisions and hatred, and that the world would be better off without it.

This hard saying of Jesus is an example of him deliberately challenging the values, the comfort zones of the culture in which he lived. Elsewhere in the Gospels, he challenges other values – the commerce that sustained Temple worship, material possessions, ritual purity, racial prejudice and militant nationalism. The challenges are never negative – Jesus is always saying, and showing in his own life, that God has something better to offer than the comfort zones – social, economic, cultural, ideological and, indeed, religious – that we humans create for ourselves.

In the case of family life, we need to remember that in those days there was no welfare state, and that the family was the social security system. Those excluded from family life found themselves isolated and impoverished. The better way that Jesus taught and lived was to engage lovingly with people outside the comfortable mutually-supportive unit of the family, loving them and sharing table fellowship with them.

And then there’s the dramatic beginning of today’s Gospel

“I came to bring fire to the earth, and how I wish it were already kindled.”

Those words have often been understood as referring to God’s judgement, but Fire has other meanings in the Bible. It is sometimes an indicator of the presence of God – remember the burning bush that Moses saw, or the pillar of fire that led the Hebrew people through the wilderness by night, or the tongues of flame at Pentecost. And Fire is also seen in the Bible as a symbol of God’s intention to purify his people – think of those verses in the prophet Malachi:

“For he is like a refiner's fire…”

We should think of Jesus as God present among God’s people, seeking to purify and perfect, yet agonizingly aware that he will be despised and rejected.

Faith, these readings suggest, need not be a cause of tension and violence. One of the themes of David Cannadine’s lecture was that for much of history people of different faiths have managed to live peacefully alongside each other and to benefit from a mutual exchange of ideas and culture. It’s worth remembering the role that Muslim scholars played in the Middle Ages in preserving the best of Greek Philosophy, Science and Mathematics and making them accessible to the Christian West. St Thomas Aquinas was significantly influenced by the Jewish scholar Moses Maimonides and by the Muslim thinker known in the west as Averroes, whose real name was Ibn Rushd and who taught that if we don’t engage critically and thoughtfully with your religious beliefs, their true meaning may be lost and we may fall into dangerous misunderstanding of God’s purposes for us.

Ibn Rushd was surely right. If faith becomes rooted in comforting human certainties, if it ceases to be self-critical, then it ceases to be faith and becomes ideology. It loses the openness to God’s gifts and to God’s purposes and becomes aggressive or defensive, and it diminishes into the conviction that the world would be better place if everyone believed and behaved just like us. Religious believers often fall into that trap, but then so do Humanists. If, on the other hand, faith is based on a recognition of the challenging generosity of God to all God’s creation, then faith becomes a willingness to move beyond the safe, the familiar and the convenient and to seek the justice and righteousness of the Kingdom of God.

It is that sort of faith of which, in the words of today’s Epistle, Jesus is “the pioneer and perfecter”. Jesus had not come to validate the divisions which we human beings are so good at creating for ourselves. Rather he came to destroy those divisions by showing the generosity of God, to encourage us out of our brokenness, our fear of others, our love of power into a new creation.

Which prompts the thought that what the world needs is not the triumph of secular Humanism, nor the triumph of one of the political ideologies into which religions so easily deteriorate – whether its Conservative Evangelicals supporting Donald Trump in the USA, radical Islamist terrorists in the Middle East or those who believe that showing disrespect to their religious beliefs should carry a death sentence  – rather what the world needs is more real faith. Real faith is costly and difficult. To live it to the full, as Jesus did, means challenging the comforting certainties of the human structures and ideologies that divide people from each other, and discovering that our comfort zone can be far, far bigger than we realized.