The church is the tip of the spear in God's work in the world. The church is where God speaks to us, meets with us, and blesses us. It is the church and her officers that possess the keys of the kingdom. It is to the advancing church that Jesus promised victory over the gates of hell. The church is where disciples are made and strengthened, where men are raised up and trained for ministry, and where long-term growth happens. The church is called to embody the culture of the kingdom of heaven. It's where God's people are molded and shaped together so that the life of Jesus is formed in and among us.
The church is the outpost on the frontier of God's kingdom work. Local churches are the epicenter of God's activity in the world and should exist in symbiotic relationship with other Christian ministries as the worship and ministry of the church flows out into holistic ministry in neighborhoods and communities. What we often call "para-church ministry" is usually a form of diaconal work. Para-church ministries have a very important role to play in God's mission of transforming society and renewing the world, but para-church ministries typically don't exist or have a transformational presence in a community unless they are connected to and overseen by local churches.
The church is the embassy of the kingdom of heaven on earth, and it is primarily through the church that God's kingdom comes and His will is done on earth as it is in heaven. A gospel presentation that says nothing about the church is a truncated, incomplete gospel. If the church is treated as an afterthought or a peripheral matter that is not really essential to the gospel, then it will be almost impossible to get people to see how important community, accountability, relationships, and pastoral leadership are down the road. An evangelistic strategy that says nothing about the church will necessarily teach people to view church as an optional accessory to their private relationship with Jesus. Not only is it unbiblical to present a churchless Christianity, but it is also confusing and misleading to new converts. As the saying goes, "What you win them with is what you win them to."