It was a priceless expression. A young couple were trekking through the frozen landscape of Alaska and they came across a frozen lake. Like it would have been for many of us, the urge to skim a stone over a frozen lake was irresistible but the result was unexpected. As soon as the stone hit the lake's icy surface a sound like a Star Wars blaster echoed throughout the valley.

Another stone was thrown and the same result. Luckily this was all captured on video and it became an instant viral hit as the combination of shock, wonder and joy on the couple's faces as they experienced this phenomenon was priceless. I was immediately tempted to jump on the next plane with my children to try to re-enact the soundtrack to the battle of Endor for ourselves. I was also struck by the poetry of the physics in play and the powerful metaphor it provides.

The science behind the incredible sound effect is due to the thin layer of ice vibrating like a cymbal the moment the stone hits it. As it bounces, it echoes, and the soundtrack it produces is caused by the different speed of sound travelling in ice and water. One small stone on this landscape sounds a keynote that produces a big and beautiful effect, and an incredible response from anyone watching. This is what I have had the privilege of seeing metaphorically as Christian foster and adoptive carers start a quiet revolution of grace that transforms their church, their town and even a nation. One keynote act of kindness to a child can reverberate around the community producing a big and beautiful wave of transforming transcending grace.

Let's take a look at how this wave can work.

Children's lives will be changed

First of all it begins with that keynote - a child's life being changed. The vast majority of vulnerable children who have experienced neglect and abuse will begin to flourish best in loving families where every part of family life becomes an opportunity for gracious therapeutic interaction. This may not happen immediately, and actually occasionally may not happen at all, and we certainly are not promising "happily ever after". However every day I come across children whose lives have been positively impacted and turned around by that one small keynote decision of a family to welcome them into their home.

Families are transformed through caring for vulnerable children

What that family may not realise at the time, is that by blessing a child in need, they too will receive blessing. For too many Christians mission is something that we do outside of our home. We send money overseas. We volunteer an evening a month to help with the homeless. We run courses to introduce people to the Christian faith. All of these are good outworkings of the grace of God, but they can still leave the centre of our lives untouched. In Britain we have an expresision " An Englishman's home is his castle." We like our space. We like to be the kings of our personal domains. But for Christians our homes are supposed to be hospitals - places of hospitality where the widow, the stranger and orphan can find help, compassion and sanctuary. When this happens something amazing echoes around the home - the love and compassion and patience and power and righteous anger of God touch us at our very core. How amazing it is to see families transformed as they pass on the love that they have received from God to those that are in need.

Churches offer the worship and mission that God deserves

When a child is blessed, and a family is transformed, this has a powerful knock-on effect into our churches. The church is not an event that we turn up to but a family that we belong to. The more our churches resemble an event or a show the less like the church they are. Scripture is replete with references to the church as "the people of God", "the household of God" (Ephesians 2:19) , and "the children of God" (1 John 5). We are told to "Love one another with brotherly affection" (Romans 12:10-13) Timothy was told not to "rebuke an older man but encourage him as you would a father, younger men as brothers, older women as mothers, younger women as sisters, in all purity." (1 Timothy 5:1-2). Church was always supposed to be family of families. Our calling as God's people is to offer God the worship He deserves and we well know "true religion that God our father accepts as pure and blameless is to care for widows and orphans in their distress". If our churches are preaching, singing and providing sacraments but failing to care for the vulnerable then our worship is inadequate. Similarly when it comes to mission we often dabble in programmatic and episodic mission where we open our church buildings to needy people for a few hours a week and then usher them out when the time is up. This does not sound like the kind of family Jesus expected us to be when he said "the poor you will always have among you." As the church becomes this family of families, wrapping around carers and vulnerable children to support and protect them, our churches sing out the kind of worship and mission he deserves.

Sadly there are challenges to the church playing this role. Firstly, many of our churches are not fostering and adoption friendly and so carers feel uncared for and unsupported and looked after children feel marginalised, making it a difficult place to go together as a family. Secondly our liturgy, our worship songs and our preaching too infrequently articulate a clear and passionate expression of the adoption theology that is the highest treasure of the gospel itself. Thirdly, many church leaders are unwilling or unable to see family based care for vulnerable children as part of the mission of the church. Our charity Home for Good is trying to tackle all three of those problems to help the church embrace fostering and adoptive families, to embrace a theology of adoption and hospitality, and to embrace the call of God to make these ministries central to their mission. When this begins to happen, our churches are transformed.

Churches offer something tangible to the cities we live in

Church leaders in the coastal town of Southampton, a city famous for its connection with the Titanic and the Spitfire fighter airplane, went to visit the city's council. They went not to complain, but to offer their service. In light of the global economic crisis, public services were being seriously cut and so these church leaders asked how they could serve the city that they loved. There was a shocked reaction from council when they discovered that the church was coming not to wag a finger of accusation at them but instead was offering a helping hand. Their biggest need was for foster carers to help look after growing number of vulnerable children that were coming into the care system. One of the leaders that went to that meeting had been in foster care himself as a teenager and so he along with a pastor who had adopted children spearheaded a campaign with a target of finding 40 foster carers for the city and over the course of the following year mobilised over 76 couples and singles to apply as foster carers. This sent shockwaves through the city and helped to transform the public opinion of the church and the gospel in the city.

We could help set off a tipping point for the gospel and our nations

Rodney Stark's popular book, The Rise of Christendom, argues that Christians ended up having a hugely significant impact on the social and moral fabric of their society through hospitality. The precursor to the Constantinian settlement that we came to know as Christendom was not a deliberate attempt to seize power but rather a grass routes transformative influence that demonstrated the compassion and grace of God in the middle of a crisis. In Stark's historical case study it was the Church's response to the great plagues of the second century that formed the tipping point for explosive growth of Christianity from "a tiny and obscure messianic movement from the edge of the Roman Empire" to "the dominant faith of Western civilization." By Stark's estimation this must have been of the order of a 40% growth rate per decade for three centuries. Stark argues that a key factor was the selfless acts of mercy and charity of Christians towards their neighbors that made such a huge impression on the population of plague-ridden Europe in the second century. In many cultures there is a growing distrust of political and religious leaders. It is often expressed that the words of our public leaders come cheaply. For Christian families, supported by their local churches to sacrificially offer hospitality and compassion through fostering and adoption is a very tangible expression of the grace of God. In fact it could easily be argued that it is a wonderfully visual lived parable of the gospel of adoption. Could it be, as the church family unites to offer needy children the lifelong love they need that many who witness this will be drawn to faith? Could it be as the church unites across a city to collectively take care of all the children that are in need of loving homes that the climate towards the gospel in a city could be transformed? Could it be that as the church across a nation collaborate together to make sure that no child is left behind or left out that we could pave the way for the same mass turnings to Christ that we saw in the second century?

Just as small stone thrown across a frozen lake in the middle of nowhere causes vibrations that bring wonder and delight, so I believe that wherever your work to care for the vulnerable is, however hard and cold and remote it is, you are joining in with the grand symphony of compassion that God is orchestrating around the world. By God's grace our lives, our families, our churches, our cities and our nations can play a part in the big and beautiful wave of transforming grace.

Dr Krish Kandiah is the founder and director of Home for Good a charity committed to finding every child in the UK that needs one a loving and permanent family. This is a version of a talk he gave at a gathering of nearly 500 leaders from 60 nations in Chiang Mai, Thailand on Saturday 13^th of February 2016.