The church is the eternal purpose of God and the goal of God’s work in time. Therefore, we must know the church in order to understand God’s plan and work in the universe. The church has a content and function in reality, and it also has an outward appearance and ground in practicality. These two aspects, one inward and the other outward, match each other and are indispensable. According to its content in reality, the church is a mystery that requires a heavenly revelation from God. However, due to the church’s degradation in the last two thousand years, the outward expression of the church in practicality has been changed beyond recognition. As a result, people either are ignorant of or filled with misunderstanding concerning the church. Thus, there is a great need for spiritual insight.