Summary: This may be one of the most misunderstood concepts in the Christian faith. A look into the word of God in Matthew brings to light the amazing calling that Jesus intends for us.
What is Church?
Matthew 16:18 (quickview)  gives us the first mention of the English word “church” in the New Testament. In all of Matthew, Mark, Luke and John this word “church” only occurs twice. Both are in Matthew (16:18 and 18:17). In the rest of the New Testament the Greek word translated "church" occurs 112 times. “Church” occurs 23 times in Acts, 43 times in Paul’s letters, and 20 times in Revelation, the rest are in the general epistles.
What is church? Actually, our English word “church” comes from two Greek words Kurios and Oikos – or Lord’s House. This has created a problem of understanding, because the word “church” in your New Testament is not from Kurios and Oikos, or Lord’s House, at all! The word the New Testament uses is always and exclusively another word: ekklasia. This word has nothing to do with a house or building at all. It applies to people and the purpose of the assembly. Ekklasia is a compound Greek word: ek – out, and kalos – called, literally ekklasia means “called out.”
This term in classical Greek is almost exclusively used to define a political assembly, like a congressional meeting or in the case of a monarchy the king and his officials. That fits Matthew’s gospel well. Matthew is the kingdom gospel. Jesus is the king and everyone in his kingdom becomes one of his officials! (As 1 Peter 2:9 (quickview)  describes us - a chosen people, a royal priesthood, a holy nation, a people belonging to God). When we come together as ekklasia, it isn’t about a holy place or holy furniture. We are called out, called to join with our King to receive instruction and conduct the affairs of the kingdom of heaven. This word is associated with one biblical book and one deutero-canonical book: Ecclesiastes and Ecclesiasticus. These books bear the name of ekklasia. They have to do with instructions for living under God’s rule and reign with His wisdom.
What is church?
What did Jesus tell us here in Matthew 16 (quickview) ? Matthew gives us a context by which to understand "church" from Jesus, our King and Lord’s own instruction. We would be wise to listen to Jesus’ explanation of what he means when he used this word ekklesia in Matthew 16 (quickview) . He has gathered with the disciples at Caesarea Philippi. The king of heaven’s kingdom has called these disciples out. He has called them to come follow him. The first thing Jesus wants to clear up with these disciples is a question of identity: his identity.
Jesus knows that we will never understand what church is until we understand who He is. We can’t understand who we are as ekklesia until we understand who Jesus is. He starts the meeting off with a question: “Who do men say that the Son of man is?” Jesus knows that people are confused about him. He knows that even his disciples are still in the dark about much of his identity, but instead of hitting them with the question directly at first, he asks them to tell him what others are saying about him. What are others saying about who I am? What is Jesus getting at?