And God said, “Let there be a vault between the waters to separate water from water.” So God made the vault and separated the water under the vault from the water above it. And it was so. God called the vault “sky.” And there was evening, and there was morning—the second day. Gen 1:6-8

Waters separated = Choose Life or Death
Dt 30:19
Waters below = fleshly life
Ro 8:7,8
Waters above = spiritual life
Jn 3:3 (born from above)
Accept or Reject
Jn 3:4,5,6; Jn 4:10,13,14

God created sky to separate the waters above from the waters below. The number two symbolized division or choice.  Man must choose between independency of ruling his own life or dependency upon God Gal 2:20 by cleaving to Him Jn 15:5.  The Gospel is the choice to believe God and live eternally with Him Rev 21:7 or reject God Rev 21:8 and be separated from Him forever Rev 20:12,15. The two waters represented two kinds of life: natural life in the earth and a heavenly one from above.  We all have been given natural life but must put our faith in Jesus to receive heavenly life 1 Jn 5:12. 

The Exodus account shared this truth of separation of life and death by the people placing the blood of a spotless lamb (symbolized Jesus’ death on the cross) on the doorpost of their homes.  Every firstborn was killed unless the blood was applied to the door Ex 12:13,29.