His life and personality became a magnet for pious legends, behind which a coherent biography is sometimes hard to discern. He is the patron saint of Edinburgh.

  Jesus (or the scribe) appears to be quoting from the Old Testament, but one phrase does not exist in any text of the Commandments: that we should love the Lord our God with all our mind.

  It is easy not to notice this phrase, and indeed Matthew, Mark and Luke don’t notice it. We know this because normally when Jesus departs from the Old Testament it is noticed, and remarked upon, and made the subject of a whole “But I say to you…” discourse.

  Not here.

  There are two aspects to this. One is what it says about the past, the other is what it says to us. The past is straightforward. The Jews have never been “people of the Book” in the sense of believing in the Bible and nothing but the Bible. They have, it is true, had a peculiar reverence for every sacred word, but they have lived not in unthinking obedience to those words alone but in a dialogue, you might even say in a relationship, with the sacred text. So the fact that “all your mind” appears here, without attracting notice or comment, must mean that it had become a part of the generally accepted interpretation of the words of Scripture. When, centuries after the Pentateuch, the Jews came across the new, Greek ways of thinking – as the Wisdom literature shows that they did – they immediately realised that this new thing called “mind” was included, no doubt about it, in the commandment to love.

  What this says to us is more important than just a footnote in the history of ideas. It is the foundation and justification of all science. God does not command the impossible. If he is to be loved with the mind, that can only be because he is lovable with the mind, or, to detheologize the language, because Ultimate Being can be related to rationally. The Gospel phrase tells us that things make sense and that we have the equipment to make sense of them.

  What does omnipotence mean? Does it mean that the Omnipotent can do anything at all? If that were true, all science would be at an end. If God willed that when I dropped a glass on the floor it would shatter, then even if God had willed the same whenever anyone in the past had ever dropped a glass, that would still not bind God. God would still be free to decide, if I dropped a glass on the floor now, that this particular glass, alone among all the glasses in history, should bounce and not break.

  Which is to say: on this interpretation of divine omnipotence, science is impossible. We cannot predict the result of an experiment, because next time God may decide differently. We cannot even lay down laws of nature based on previous experience, because to call a law a “law” is to claim to be able to bind God, which is blasphemy.

  This is not merely an academic quibble. When the 11th-century Muslim philosopher al-Ghazāli propounded this very idea, it captured the mainstream of Islamic thinking and led to the virtual suicide of science in Islam and the abandonment of rational thinking about the physical world, as being unnecessary, or sacrilegious, or both.

  We are saved from this by this one little phrase in the Gospel, about loving God with all our mind. It is more than mere permission, it is a command to understand, to go out and do science, and it was followed whenever Christians had leisure to think. It led to the dazzling 13th-century renaissance and the birth of modern science, and we are still living through its consequences.

  As for divine omnipotence, this is not the place to go into it in detail, but the answer to al-Ghazāli must surely be that God can indeed make the glass bounce, but God cannot make the glass bounce and still be God, since to break the laws and regularities of nature whimsically and without reason would be to abandon lovability-with-the-mind. This is exactly the argument that theologians use against pointless or frivolous miracles, but it applies to science as well, and to the possibility of doing science at all.

  The late 14th and early 15th centuries saw a miraculous outpouring of mysticism and spirituality all over western Europe, encompassing The Cloud of Unknowing, Walter Hilton, Julian of Norwich, and even the maddening Margery Kempe. Much of it was lay, and even Thomas à Kempis, who became a priest, belongs not to any of the great monastic or preaching orders but to the Brethren of the Common Life, a movement which started in the Netherlands and Rhineland in the late fourteenth century. The birth of the movement was the teaching of Gerhard Groote, who preached and taught a simple prayerful way of life which people could follow in their own homes. Groote shared most of his own large house in Deventer, in the Netherlands, with a group of devout women who lived together as a community (without taking formal vows), and Florentius Radwijns, one of the cathedral clergy and a follower of Groote’s, then hosted a similar community of men. The Brethren of the Common Life aimed to live a communal life in imitation of the simplicity and poverty of the earliest Christians, devoting themselves both to contemplation and to active works. In the time of relative ecclesial peace which preceded the Reformation the Brethren were allowed to grow and develop largely without too much interference. In due course a progression was also established whereby those Brethren who desired a more formal commitment founded, or joined, houses of regular Augustinian canons or canonesses.

  Thomas à Kempis himself was born in Kempen, a small town not far from Cologne. He went to a school founded by Gerhard Groote, and in 1399 became a member of the recently founded Augustinian house of which John, his elder brother, was the first prior. He remained a member of this community for the rest of his life.

  It was a custom of the Brethren to make collections of sayings on spiritual topics, and Thomas followed this practice from his schooldays onwards. Thus some of the Second Readings from the Imitation that we use in the liturgy read almost like a sequence of “bullet points”. In a sense this is the best use of the Imitation – as a bedside book to be read one chapter out of each night, as Monsignor Ronald Knox did in his later years. Thomas à Kempis manages, in each short chapter, to propound a theme or even sketch a situation, and to bring out of it a moral or a conclusion, food for the spirit. Knox tells us that in the days when English Protestants treated The Pilgrim’s Progress as a sort of extra book of the New Testament, The Imitation of Christ was practically the Catholic equivalent. But that does not make it a warm bath to sink oneself into. As Knox puts it:

  “The whole work… is a sustained irritant which preserves us… from sinking back into relaxation: from self-conceit, self-pity, self-love. It offers consolation here and there, but always at the price of fresh exertion… Heaven help us if we find easy reading in The Imitation of Christ.”

  In the earliest centuries all vestments were white – the white of baptismal purity and of the robes worn by the armies of the redeemed in the Apocalypse, washed white in the blood of the Lamb. As the Church grew secure enough to be able to plan her liturgy, she began to use colour so that our sense of sight could deepen our experience of the mysteries of salvation, just as incense recruits our sense of smell and music that of hearing. Over the centuries various schemes of colour for feasts and seasons were worked out, and it is only as late as the 19th century that they were harmonized into their present form.