Last Sunday I tackled the topic of the Holy Spirit and how important that Person of the Triune God is to the church, or, ekklesia.(You can hear the full message here.)
I the Bible study guide of Acts I wrote for LifeBibleStudy, I said it this way:
A body without a breath is only a body. A church without the Holy Spirit is only an interest group. The difference between the Ekklesia as Jesus commissioned it and any other service organization or religious group is the presence of the Holy Spirit in the lives of those who assemble as the "body of Christ." Churches can do good things for its members and for the community, but without the presence of God's Holy Spirit it is not the Ekklesia.
Read the Acts of the Apostles again if you are a follower of Jesus. Heck, read if you don't trust Jesus and see what's up. Watch and listen to the roll the Holy Spirit plays in the explosive movement of God's People called the church. Watch and listen to how you are the church and see how they match.