In order to more fully understand this question, we first have to take a step back and see the bigger picture into which the church fits. This bigger picture includes the entire Bible and the entire world throughout all of time.
God did not need to create, but He did. He decided to create a vast and magnificent universe within which and to which He would display His glorious nature. Human beings occupy a unique place within this creation as we alone are made in God’s image. We were His people and He was our God and everything was “very good.” The knowledge of the glory of God covered the whole earth as the waters cover the seas.
And then came the Fall and the human race was plunged into sin and death under the headship of our father, Adam. Even the creation itself groans under the weight of the resulting curse. What would become of God’s glorious creation and His plan to display His marvelous nature? Most pointedly, what about the image bearers – the humans who were intended to live in perfect fellowship with God but now are in active rebellion against Him, enemies of Him in thought, word, deed, and affection?
From the moments immediately following the Fall, God initiated His eternally-planned rescue and restoration mission. Immediately He begins to speak of One who is yet to come. This One will again set things right, and after His ministry, there will again be a perfect, New Heaven and Earth, filled with a New People and once again the knowledge of the glory of God will fill this world and this people. This One who is to come will take the punishment of the curse; He will break the power of the curse; and His work will eventually eliminate the effects of the curse altogether. But who is He? And how will all of this work?
The Old Testament told us through shadows and types as God began to call together a people for Himself. Nevertheless, the details remained a mystery. Until He came. Then, as the book of Ephesians explains, the ins and outs of this mystery were made known. The church today serves as the canvas upon which the “manifold wisdom of God is made known to the rulers and authorities in the heavenly places.” (Eph. 3:10) It is the new temple, “which is the dwelling place for God by the Spirit.” (Eph. 2:22) In it is great glory for the Father (Eph. 3:21) as all of the creation looks at the church and sees the outworking of the mystery of God: the saving, cleansing, and transforming work of Christ and His reign over all things (Eph. 1:9-11; 3:6-8). Put simply, the mystery of God is Christ and it is made fully known in the church.
God sees the church as a living, breathing, visual aid. We are a display for all to see of the Christ-focused wisdom and power of God – bringing some of the fallen sons and daughters of Adam under a new head, Christ, and with them again making a beloved people. We were His enemies, and now we are His friends and children. We loved the world. And now we love Him, to the praise of His glorious grace. We lived for our own purposes, and now we live for His glory in our own midst and among the nations – now and into all eternity. And all who look at us – be they other people, or spiritual beings in the heavens, are supposed to see and marvel at the greatness of God who planned such a wonderful, mysterious mission.