In the middle of the long reign of Queen Victoria there was a British Member of Parliament who was a Christian committed to defending those who were the victims of society. He found himself grieved by the heavy loss of life amongst British merchant seamen – often a thousand deaths a year – largely caused by greedy owners overloading their vessels to the point where they easily sank.

He knew of a simple invention that, if it was made compulsory, could prevent these 'coffin ships' from sailing and so, for ten long years, he battled in the Houses of Parliament for the law to be passed. He eventually won in 1876. His name was Samuel Plimsoll and the invention couldn't have been simpler: an official, very visible and permanent mark on the side of a ship indicated the maximum load that the ship could carry.

If this mark – it soon became known as the 'Plimsoll line' – disappeared below the surface of the water, the ship was illegally loaded and must not sail. Because these were the days when 'Britannia ruled the waves', the Plimsoll line came to be used universally and, thanks to its existence, an uncountable number of lives have been saved.

Now the reason that Plimsoll came to mind is because I have just revised my book on the Ten Commandments and I find in them a comparable standard for our lives. What Plimsoll sought to apply to ships was a clear, enduring, life-saving way of setting limits that, even under pressure, must not be broken. The Ten Commandments do the same: they are, if you like, the Plimsoll line for our existence. If we ignore them or let them sink below the waves of life, then being in some way drowned or shipwrecked is inevitable.

The Ten Commandments set out in ten clear clauses, few in words but infinitely wide in application, our Maker's limits for the great areas of our life. In these rules we find guidance on how we relate to God, how we are to use our time and how we relate to our families and to those we live amongst. Despite the fact that they were given in a culture profoundly different to any we live in today, the Commandments cover every aspect of human life. At one level, the Ten Commandments are the simplest and clearest of guides; yet at the same time they have a limitless depth and breadth in what they cover.

In fact, the Ten Commandments serve a double purpose. They serve as a judge: they set out the limits for how we should live and inevitably, given the inclination of human beings to do wrong, they force those who consider them seriously to acknowledge their guilt. Morally, we are all well below the waterline but there is a mercy in their exposure of our failure because it should drive us to seek God's forgiveness, something found fully only in Christ.

Yet if the Ten Commandments are a judge, they are also a guide. They lead us to the cross but they also lead beyond it by showing those who have been forgiven in Christ how to live in order to honour him. The Commandments are the standard that we all need and that, this side of eternity, we always will.

Yet if the standard of the Ten Commandments is vital, teaching about it has never been so urgently needed. I have been preaching on the Ten Commandments for over a quarter of a century and I have observed clear changes in how they are viewed.

Within living memory, they were honoured publicly as rules for life and to break them publicly was something done with at least embarrassment and possibly shame.

Then, with time, they became downgraded to being merely 'guidelines' or 'advice'; things that could be politely respected but then ignored. Now, if they are known at all, the Ten Commandments are openly treated with scorn or amusement. To take the plainest of the Commandments, we now find that such things as lying, adultery, hatred and greed are considered part of any normal human life.

Despite their dismissal, the stark fact is that the Ten Commandments have not lost their relevance. Oh, things have changed. Theft may now be achieved through a computer keyboard rather than picking a pocket; 'bearing false witness' may now occur on the Internet rather than in local court, and 'adultery' may now be masked under many more sophisticated names.

Yet the judgement the Commandments make on us still stands. It is not for nothing that the Ten Commandments were originally given engraved in stone: they are a rock which resists change no matter how angry the waves of an ever-changing culture break against them.

In describing the Ten Commandments like this, I am aware that they could be seen simply as a burden. Yet what is fascinating and perturbing is the way that if, as society has done, the Commandments are rejected, the result is not a state of no morality but instead an alternative morality. We see this today: surveying our present world we find that we have a culture which is in fact all too ready to pass judgement, where today's joke may be tomorrow's taboo and where a failure to signal your virtue is an admission of guilt.

Our 'liberal' culture is, in reality, cruelly illiberal. Indeed, because morality is no longer anchored to anything except sentiment, who knows what new rules will emerge and how we will fare under them. Separated from a fixed standard, virtues can become vices at a moment's notice. If we are not all guilty at the moment, be warned, we may soon be.

So although the Ten Commandments are often dismissed as harsh rules that constrain who we are, the irony is that in fact they are liberating. In them we see God saying in effect that if we operate within these guidelines, we will flourish as we are meant to. So it's time to return to the Ten Commandments and think about how they should work in our age.

Samuel Plimsoll knew that without a permanent standard, the pressures of life would result in ships sinking. He would doubtless, too, have agreed that without moral standards the same fate occurs to individuals. And, indeed, to nations.

Can I encourage you to purchase a copy of my new revised book on the Ten Commandments and renew and realign your thoughts, words and deeds?

Rev Canon J John is an evangelist and the director of the Philo Trust. Find him online at www.canonjjohn.com