It was the best of times, It was the worst of times ... It was the season of Light. It was the season of Darkness. It was the spring of hope. It was the winter of despair. We had everything before us. We had nothing before us. We were all going direct to Heaven. We were all going direct the other way.

With these immortally paradoxical lines Charles Dickens introduces his epic novel A Tale of Two Cities. The contradictory sentiments they invoke point at the coexistent extremes of life in so-called 'enlightened' eighteenth-century London and Paris, at a time just before the French Revolution. These lines hint at the contrasts and tensions that will unravel in the book, and the conflicting values that will be portrayed. Love and hate. Wealth and poverty. Good and evil.

They make for an apt description of another time in history, too; one where Light and Darkness, hope and despair smashed into each other, and the world was changed forever.

If ever there was a paradoxical moment in time, it was three o'clock on that first Good Friday afternoon outside the city of Jerusalem, atop a hill that had been given the nickname 'the Place of the Skull'. It was the middle of the day, and yet it became the middle of the night. It was humanity's darkest hour, and yet divine love never shone brighter. An innocent man had been found guilty and was being given his – or, rather, everyone else's – punishment. A man screamed out to God, asking why he had been abandoned, and at the same time the curtain in the Temple was ripped open, welcoming the world into the very presence of God. The death and distress of the one offered life and hope to the many. To the world, it looked like utter defeat, but in fact it was God's greatest victory. In this picture of abject weakness, the power of God is revealed.

The cross of Christ has to be the biggest paradox in Scripture. It is so difficult to grasp that it is described as a stumbling block to faith to some, foolishness to others, and yet for some of us it is the turning point of history and the foundation of our faith.

So why do Christians make such a big deal about the cross? How can an event in a forgotten backwater of the Roman Empire 2,000 years ago have any significance for a world facing Islamic State or reeling from a plane crash in the alps? Could an eternal God be so concerned about the temporal affairs of humans as to make history turn around one particular man, one death, in this way?

There have been various turning points in history where specific events in very particular situations have had a global impact. Whether it is patient zero in the Ebola pandemic, or the murder of a man looking for a hospital, which would spark World War I, our history books are littered with examples of seemingly minor events that have huge repercussions. In the field of physics, chaos theory proposes that small changes in complex systems can have huge and unforeseen consequences. The classic example is of a butterfly flapping its wings in one hemisphere, resulting in a hurricane being generated on the other side of the world. Some argue that if the tuning between weak and strong nuclear forces in atoms were off by the tiniest amount – 1 in 10,000,000 – then no elements heavier than hydrogen would be able to exist. So science is certainly willing to consider that a lot could hinge on something that seems inconsequential; that something very particular can have a significant universal effect.

But what is it about the cross of Christ that makes it so significant? Part of the answer to this is to do with who it was that was on the cross. It was not just anyone who took a wrong turn down the wrong street looking for Sarajevo Hospital and thus came within range of Gavrilo Princip's gun, but Archduke Franz Ferdinand himself. It was the assassination of the heir to the Austrian Empire which ignited the atrocities of World War I. Similarly, this was not just anyone dying on a cross. The Romans used crucifixion widely as a means of public execution, so it was not crucifixion that was unique. Rather, the identity of the crucified person holds the key. Remembering that Jesus was the unique God-Man sheds light on why his death matters. As hymn-writer Isaac Watts put it, ''Tis Mystery all, the Immortal dies'. What a paradox: the eternal God, the author of life, experienced the worst of deaths.

Unlike the death of Franz Ferdinand, however, the cross was no accident of history. God had been building towards this moment from eternity past and had written markers into human history to guide us to the right understanding of this event – this was no ordinary death. Imagine watching the ultimate heist movie with, of course, a priceless diamond arriving at a museum. The alarms are set to cover every inch of the display hall, and weight sensors are sensitive to the nearest gram. Extremely careful planning is necessary by the prospective thieves so that at the decisive moment an unnoticed switch or substitution can occur. The diamond has to be replaced by something that is exactly its weight, or all the alarms will sound and the caper is over. This image gives us an inkling of what was going on when Jesus died on the cross. This particular substitution had been planned in minute detail since before the beginning of time itself, and signposted throughout the Jewish Scriptures.

You can see those signposts from the moment that sin entered the world. God had promised that if humanity sinned, death would result, but in the Garden of Eden the first thing to die after the fall were not sinful human beings but animals, sacrificed to provide fallen people with the clothes they needed to cover over a nakedness that was no longer appropriate in a world contaminated by sin. We see in the story of Abraham's attempted sacrifice of his son that the ram caught in a thicket which took the place of Isaac was a signpost to Jesus, who would be described as 'the lamb of God that takes away the sin of the world' (John 1:29). We see in the story of Moses that the Holy of Holies in both the Tabernacle and then in the Temple was barred to all but the High Priest, and then only on the right day and with the shedding of sacrificial blood. We see in the story of Job that whether for a cosmic purpose or not, there are times when an innocent person will suffer. We see in the story of Jonah that when the sailors threw God's prophet ostensibly to his death, that was when they were saved.

All of these Old Testament stories; and many more along the way are signposts to the Cross of Jesus, the place where we see resolution to these stories. God was building up to the exact moment that his Son Jesus was born in Israel, at a time when the country was under Roman occupation. The death of Jesus involved the ultimate substitution. Jesus' death did not just satisfy but fulfilled the sacrifice system set up in the Old Testament. It satisfied God's righteous anger not just once but for all. It paid for the sins of the entire world. The death of Jesus was not an isolated and random event in a forgotten corner of the Roman world. The cross of Jesus is the place where all of God's plans come together. X marks the spot: this place, this time is where God is resolving the great paradox of history. God uses the tiny details of history to solve the riddle of the universe, demonstrate his perfect love and redeem his broken world.

The cross of Christ is both the low point and the high point of human history. We see humanity's darkside in the conspiracy to execute Jesus on trumped up charges. We see evil at work in the unrelenting cruelty of crucifixion as a means not just of barabaric means of torture but also a public relations exercise in showing the futility of challenging the supremacy of Roman military power. From this perspective it is hard to fathom why their could be anything good, about good Friday. But on the cross we also see the grace and majesty of God in equal measure. We realise that Jesus' death was no accident, but rather the deliberate choice of Jesus to enter our world, rescue us from the consequences of the mess we have made of our lives and our planet. Jesus fulfilled the Old Testament stories so that we could be forgiven for our sins, reconciled with God and adopted into his family. That first Good Friday was simultaneously the worst of times and the best of times, let's make sure we celebrate it well.

Dr Krish Kandiah is the founder of Home for Good and a Contributing Editor to Christian Today. He is the author of Paradoxology: Why Christianity was never meant to be simple.