15/06/2015 06:21 BST | Updated 15/06/2016 06:59 BST

The Church and Magna Carta

"So would it be fair to say that if the Church hadn't been involved in politics in the early 13th Century, there would have been no Magna Carta?"

It was the first pause in our conversation, as Nigel Saul, Professor of Medieval History at the Royal Holloway, subjected my question to proper academic scrutiny. "If you were to press me for a simple yes or no answer", he replied carefully, 'I'd have to say "yes".

We'd been discussing Stephen Langton, the Archbishop of Canterbury at the time of Magna Carta, whose shuttle diplomacy between King John and the barons had played such a significant part in the events of June 1215. We'd also been reflecting on the churches' role in disseminating the charter - a job that was uniquely entrusted to churchmen as honest brokers rather than to the sheriffs who were (rightly) perceived as the king's men. We were noting that even today, two of the remaining four originals of the famous document are held in Cathedral libraries.

Only one of the 63 clauses in Magna Carta was clearly drafted by the Archbishop, Professor Saul told me - clause one, in which it's asserted that "The English Church shall be free"; the rest had been a classic committee job. But how about the origins of the key ideas in the document - the rule of law, the limits placed on the king's authority, the extension of rights to "all free men"? What was the philosophical foundation of those clauses that have since given the Magna Carta both its actual and its mythical status as "the greatest constitutional document of all times - the foundation of the freedom of the individual against the arbitrary authority of the despot" (Lord Denning, 1965)?

For anyone who knows and loves the Biblical book of Deuteronomy as I do, there's a sense of deja vu when it comes to reading the Magna Carta. For although there is controversy about exactly when Deuteronomy reached its final form (most probably in the 7th or 6th Centuries BC), there is no controversy about the meaning of two passages which are especially pertinent in the context of "1215 and all that".

The first (what we might currently describe as a Fifa clause) relates to the establishment of a proper legal structure:

"You shall appoint judges and officials... in all your towns that the Lord your God is giving you, and they shall render just decisions for the people. You must not distort justice; you must not show partiality; and you must not accept bribes, for a bribe blinds the eyes of the wise and subverts the cause of those who are in the right. Justice, and only justice, you shall pursue..." (Deuteronomy 16:18-20)

The second (which draws out the classic leadership temptations of money, sex and power) relates to limitations on the power of the king:

"One of your own community you may set as king over you... He must not acquire many horses for himself... and he must not acquire many wives for himself...; also silver and gold he must not acquire in great quantity for himself. When he has taken the throne of his kingdom, he shall have a copy of this law written for him in the presence of the priests. It shall remain with him and he shall read in it all the days of his life, so that he may learn to fear the Lord his God, diligently observing all the words of this law and these statutes, neither exalting himself above other members of the community nor turning aside from the commandment, either to the right or to the left..." (from Deuteronomy 17:14-20)

When taken together with the role of the Biblical prophets in challenging the bad kings of their day for their failure to obey God's law - a noble line from Elijah to John the Baptist - it's not difficult to recognize the philosophical, indeed theological, roots of Magna Carta, as transmitted through contemporaneous theologians like Stephen Langton himself.

The relevance of this to today's debates - where the concept of universal rights is often assumed to be the product of the secular Enlightenment, and 'religion' (whatever that is) is regularly regarded as a problem not a solution - can hardly be overstated. The call on the Church to continue in the footsteps of Archbishop Langton is well articulated in the fourth of the Anglican Five Marks of Mission: a call 'to transform unjust structures of society, to challenge violence of every kind and pursue peace and reconciliation'.

And as I (along with thousands of others) plan to travel to a muddy field in a far-flung corner of my Diocese in the early hours of Monday 15 June 2015 to celebrate the 800th anniversary of the "greatest constitutional document of all time", I do so with renewed confidence in the role of the Church and the Judeo-Christian tradition in shaping the values of our democracy, and liberal democracies all around the world.

The Rt Revd Andrew Watson is the Bishop of Guildford