Dear King Charles,

In your coronation oath you are going to solemnly promise "to the utmost of your power maintain the Laws of God and the true profession of the Gospel". And to "the utmost of your power maintain in the United Kingdom the Protestant Reformed Religion established by law". These are solemn promises. We pray that our gracious God will help you fulfil them.

There have been two King Charleses before you. The first was the only king in English history to have been executed by parliament. We pray that no such fate – or even a lesser dethronement awaits you!

One of Cromwell's chaplains who bravely objected to the execution was the Rev Thomas Manton, of Covent Garden, who was also instrumental in the return of King Charles II to the throne. He became a royal chaplain but when he refused the deanery of Rochester, he ended up being imprisoned for his ministry.

King Charles II, despite his promises, persecuted both English Puritans and Scottish Covenanters. I hope and pray that King Charles III will have a better history than your predecessors! Surely we have passed the time when kings were beheaded and Christians 'cancelled'?!

Speaking of Thomas Manton, I came across a wonderful sermon of his on Psalm 119 verse 46, in which he says, "I will speak of thy testimonies before kings, and will not be ashamed".

I thought I would share some of his wisdom which is suitable for us all on this occasion (you can read the whole sermon in his works, volume six, p 486).

Manton argues that "there are some kings that have not submitted their crowns and sceptres to the King of kings" such as "pagans and wicked princes who can neither endure the truth, nor those who profess it". Given your coronation oath I am sure that you are not included in that not so illustrious body.

He goes on to argue that "there is nothing so necessary for kings, princes and magistrates to know as God's testimonies". Your late beloved mother, our late lamented Queen, knew the truth of this and was explicit in her affirmation of it. I hope and pray that you will follow in her footsteps.

Your task is a difficult one – one which you have been waiting for a long time. And one which is not made any easier by the confused and confusing times we live in. Manton argues that what makes a good king is "trust and dependence upon God" – which is why all Christians in your realm will mean it when they pray "God save the King".

What will make your reign "happy and glorious"? Again, Manton nails it. Success and acceptance come from the rulers obeying God so that there is a blessing in having "holy governors" and a reinforced stability and authority in the land.

For all of us, including the highest in the land, "the fear of God, or a deep awe and reverence of him," is when we are "more afraid to offend God than to suffer from man".

To modern ears the teaching of Paul in Romans 13 seems strange, but your late mother knew the truth of it.

Rulers have been "established by God" and are "God's servants". Yes, you are a servant of the people, but above all you are a servant of God. May it be that when your reign comes to its inevitable end He will say "well done, good and faithful servant".

Which is why it is so important that you keep your promise to uphold "the laws of God and the true profession of the Gospel". Again, to quote Manton: "We must not be ashamed to own the testimonies and ways of God, before any sort of men in the world".

Manton reminds us of five things to 'fortify' us against being ashamed of God and his ways.

1. "The short continuance of this world's glory." While people will of course pray for you "long to reign over us", this life is short and it won't be that long before you or any of us enter into the presence of the King of kings.
2. "God is the fountain of honour. All things and persons receive an honour by having relation to him."
3. If your hearts be sincere with God, you will not be ashamed of his ways.
4. The eternal recompense. "Those that honour me I will honour" (1 Samuel 2:30).
5. "The judgement of the world is not to be stood upon. Why should we desire the applause of the blind ungodly world, or make any great matter of their contempt and scorn?"

I am so delighted that the idea you had a couple of decades ago of being the 'defender of faith' rather than Defender of the Faith, has been dropped. The former would have been meaningless; the latter has substance! It is possible to defend the Christian faith while upholding the religious and civil liberties of others. While you are the King of all your subjects, as your coronation oaths affirm, you are a Christian king, anointed to serve Christ and the true profession of the Gospel.

As you undertake this solemn ceremony and awesome responsibility, I want to assure you that the millions of your subjects who are Christians will pray for you according to the words of Paul to Timothy: "I urge, then, first of all, that petitions, prayers, intercession and thanksgiving be made for all people – for kings and all those in authority, that we may live peaceful and quiet lives in all godliness and holiness. This is good, and pleases God our Saviour, who wants all people to be saved and to come to a knowledge of the truth" (1 Timothy 2:1-4).

God save the King!

Yours etc.

A servant of the King of Kings,

David Robertson

David Robertson leads The ASK Project in Sydney, Australia. He blogs at The Wee Flea.