What Makes a Church a Church?

Did Jesus plan for His church to be imperfect?
He certainly planned for it to filled with imperfect people, saved sinners.
He planned for it to be lead by mature but still imperfect people. One of the most prominent church leaders of all time, Paul, proclaimed that he was the chief of sinners.
When the Holy Spirit wrote to many of the churches of Christ in the first century He did so because they were not getting church right. There is more in the letters of the New Testament about what was wrong with those churches than what was right.
Despite all this God regards this imperfect church as His church. So, what makes a church a church? I have some ideas from scripture. I hope you do as well and are willing to share them with me. What do you think? I will share my perspective in my next posting.