"The central message of every other religion is – 'you are saved by what you do, by living in this way.' That means that ultimately, it doesn’t matter whether the incidents in the Buddhist or Muslim Scriptures really happened or not. It doesn’t matter whether Buddha or Muhammad did this or that miracle or not. What saves us is not what they did but by what they said and taught. We are saved by following the path to God they laid out.

But the central message of the Christian documents is the very opposite of that. It is – ‘You are saved not by what you do, but by what he has done. He has entered history and lived the life we should have lived and died the death we should have died. This means atonement has been made. This means the kingdom of God has broken in to the world and our lives and will change the course of history.’ In other words, if we are to be saved by grace, the historical events must have happened. Ever notice how the gospels give 30-50% of their time to treat just the last week of Jesus life? What kind of biography spends that much time so disproportionately? The gospel writers believed it wasn’t the example and teaching of Jesus, but his saving work in history for us – his death and resurrection – that saves us.

Therefore the historical reliability of the gospels is crucial for the very message of grace. If you get ‘spiritual meaning’ – a general inspiration – without understanding the central message, then you are settling for crumbs."

Tim Keller, Gospel Christianity, Redeemer Presbyterian Church, p. 6.