There is a debate raging (and it has been going on for a long time now) about the role of church in society in relation to culture. Many different models have been put forward over the years of what it means for the church to engage the mission of God to a broken world. Some say that the church is primarily to be the place where salvation is found as the people of God come together to grow in Christ and be strengthened. In other words, church is for believers. Others say that church exists for the lost and that the church should be oriented toward people who do not know God. Some try to say that it is the church's job to reform society or even to take over culture. Others say that the church should stay out of all of that and just focus on teaching people how to live for Jesus while preaching the Word and engaging in worship.
This is not an academic debate. Where you stand on this issue will probably speak to how you see the church and how you take part in the life of your church and how your church participates in its community. Is the church a citadel standing against the forces of darkness? Is it a missionary band? Is it a refuge against the encroaching evil of the world? Is it a lighthouse? Is it a town square where everyone can gather? You metaphors dictate your mood regarding the church and how it functions.
While the mission of the institutional church is to preach the Word and produce disciples, the church must disciple Christians in such a way that they live justly and integrate their faith with their work. So the church doesn't directly change culture, but it disciples and supports people who do. Another balance has to do with society's cultural institutions. Rather than taking them over, or avoiding them as a corrupting influence, or treating them with indifference---Christians are to be a faithful presence within them.
The church cannot do everything nor should it. I have heard people say that the reason that the government is involved in social issues in America is because the church abandoned its duty. That is one of those somewhat true statements. Yes, the church did retreat in large part from social justice issues around a century ago, but the government also amped up what it means to care for the poor far beyond what the church would ever be capable of doing. The fact that people are on welfare is not necessarily because the church failed to take care of the poor. Rather, it might be because the church failed to effectively tell an alternate story about what true compassion is and what it looks like to be a just society. The problem with poverty in America is not just that the church does not give enough to the poor, but also because Christians have not engaged the social, political, and educational realms with a strong enough vision of how we are to best live life on this planet. So, instead, we have a lesser story that has taken over in absence of the true story that God would have us live out. Our job is not to eradicate every problem in the world, but rather, to live out a different story and give witness to the One who will make all things new.
The role of the church is to help people live out the gospel of the Kingdom in all realms of life. It is to be a "faithful witness" to Christ and His reign and rule in all spheres. The church can only do this as it disciples people to live "Christianly" in every sphere of life, whether that be at work, at home, in the community, or in relationship with the church. We should help people think through how they can be salt and light and both proclaim and demonstrate the gospel of the Kingdom. We are to be yeast, a seed, a quiet but unyielding witness, a faithful presence in the midst of a world going mad. Of course, the church collectively gives witness to the truth of Christ and can work together to do much good in the world as it proclaims and demonstrates the gospel, but the greatest impact that the church can have is when it disciples its members to live out the life of Christ by loving God and loving people everywhere.
The Incarnation of Christ that we celebrate at Christmas is all about Christ breaking in to our world in a cosmic invasion to bring the good news of the Kingdom of God to us - to reconcile us and all of creation back to God through sacrificial love - love that led to the Cross and triumphed through the Resurrection. We, as the people of God in the church reflect the Incarnation when we live redemptive lives in the world - not trying to take over, but attempting to live subversively as citizens of a different order altogether.
The revolution begun in Bethlehem continues and the church is as the center of it.