This is one of the foundational truths of the Bible and is profound. Without an understanding of this teaching, you cannot understand the problems of the soul or the world.

Death is the main problem that mankind has, and the cause of death is sin.

In Genesis 3, God warned Adam that if he ate from the tree of knowledge of good and evil "you shall surely die." Elsewhere the Bible says that "the penalty of sin is death". Through Adam's sin, mankind was corrupted with a sin nature, or Original Sin, and therefore all of mankind was condemned to the curse of death, both physical and spiritual. In the Old Testament, God required a substitutionary animal sacrifice for the overlooking of sin (since life is in the blood, there must be the shedding of blood to atone for sin), but it never permanently solved the sin problem.

But God had a plan to redeem man's soul from His own punishment, and this was through the sacrifice of His Son, Jesus Christ. Jesus said He came to give us life, eternal life, and solve the only problem we all have - the forgiveness of sin.

Just as through one man's act of disobedience, Adam, all men were cursed, through one Sinless Man's obedience, Jesus Christ, all can be forgiven and made righteous.

The Gospel
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The first step in the Salvation of your soul is to admit you are sinner, completely unable to solve this problem of your heart on your own. Then believe that Jesus Christ, who is God, died on the Cross so your sin could be forgiven, and by His rising from the grave, He guarantees Eternal Life to all who believe.