The Apostle Paul in Colossians 1:18-19 says, Jesus Christ is the head of the church. He is the source and authority of the church. Without the head, the body will die.
When you say the church is the body of Christ, three ideas come to mind. First, there is the idea of life. Without Jesus Christ, the church does not exist. Without the church, the life of Christ on the earth could not be known. Both are necessary for life.