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"And the LORD God commanded the man, saying, 'You may surely eat of every tree of the garden, but of the tree of knowledge of good and evil you shall not eat, for in the day that you eat of it you shall surely die'" (Genesis 2:16-17). 
"And they made his grave with the wicked and with a rich man in his death, although he had done no violence and there was no deceit in his mouth.  Yet it was the will of the LORD to crush him..." (Isaiah 53:9-10). 
"For our sake he made him to be sin who knew no sin, so that in him we might become the righteousness of God" (2 Corinthians 5:21).
 Death is a part of life.  It is all around us.  Even in the womb, life is fragile and requires lots of special care.  Likewise, after a new house is built, it immediately begins to deteriorate due to rain, wind, insects, and just by general use.  We are so used to death, decay, and deterioration that we may not stop to think: death is not normal.  Death is a result of the curse of God upon His creation for their disobedience toward Him.

When we understand death as a curse, it changes our understanding of several important things surrounding the cross and the death and resurrection of Jesus Christ.  Death is crucial to understand if we are to grasp the significance of the resurrection.