What is church? The more telling question is, Who is church? And the biblical answer: All persons who have been united to the Lord Jesus Christ in his life, death, resurrection, ascension and return in power and glory at the end of this age.
This answer is not the result of a survey of people who go to church. Church is not, in the first place, a thing or event we go to. In its essence, the church is people. The people who are the church belong to Jesus Christ. They belong to him because God the Father chose them in Christ from the foundation of the world (see Ephesians 1:3-4). They belong to him because God the Father gave them to God the Son (See John 17:6).