It only takes a few days without sun for a plant to begin to die. Photosynthesis immediately halts and within a few weeks of not having the sun, all smaller plant-life would cease. One variable was changed. Just one. The sun sustains life on this earth. If the sun were to dissapear, a chain reaction would occur and eventually the human race would cease to exist. One seemingly small change, one massive result.
Let's take a look at it in another way: We have a Great Creator: Jesus Christ. The only times we feel warmth and see light in our lives is because He is in it (whether we realize it or not). Jesus is the "light and life of the world... a light that is endless that can NEVER be darkened"(Mosiah 16:9 caps and bold added). We must walk by this light, otherwise we cannot see the path in front of us. Unlike the solar system's sun (which one day could burn out), the Eternal Son (Jesus Christ) will never fail us. Never do we need to worry about one day waking up and the Son not being there. He will continue to shine forever!
Sometimes we make choices, however, that distance us from the Son. We knowingly and willingly reject His light by our actions. When we do such, we do not have the benefits of the Son-light in our lives. Consequently, spiritual photosynthesis stops and within a few days we are filled with despair and darkness. We starve our spirits of the much-needed nutrition that can only be obtained from Jesus Christ. Eventually our spirituality would die. We cannot let this happen! Let us turn our faces again to the Son and feel of His warmth and light. Repentance is granted to all who "come forth with broken hearts and contrite spirits"(3 Nephi 9:20). Every living creation on this earth knows that life will stop without our sun, let us see the wisdom in that and never go a day without the Son.