God created the Sun, the Moon, the stars and the Earth and the planets to illustrate His spiritual truths so we could better understand our relationship with Him and how necessary He is to our spiritual solar system.
Life itself wouldn't be possible without the Sun! Without the light of the Sun we'd be in total darkness except for starlight, just as without the Lord we would be in almost total spiritual darkness. Without the warmth and heat of the Sun's rays, we'd also freeze to death, just like without the Lord we'd be dead cold spiritually! Without the Sun's rays there would be no photosynthetic process which causes the plants which provide our food to grow; so we'd die spiritually of hunger without the Lord to feed us spiritually. Without the Sun's gravitational pull on the Earth, instead of staying in its well-planned orbit, the Earth would go wandering off through space. So without God's guidance, His gravitational pull on us in the spirit, we too would certainly get out of the well-planned orbit of His Will, and we'd go wandering off into the darkness of spiritual space!
If the Sun has that much power, think how much power our spiritual Sun, God, has and how much we need Him!