Death would never have come into the world if it had not been for sin. God warned Adam and Eve:

Genesis 2:16-17 

"And the LORD God Commanded the man, saying, of every tree of the garden thou mayest freely eat: But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die."

We were meant to live forever until mankind ate of the tree of the knowledge of good and evil. And what is there in the world today? Good and evil.

James 1:15 

"...and sin, when it is finished, bringeth forth death."

Romans 6;23

For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord.

God had to send an atonement for our sins. A passage way to be with our Holy God who created us in his image.

John 3;16

For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.

God sent his only son to willingly sacrifice his own life for our sins so that when we truly believe he died on the cross for us our names will be written in the Lamb's Book of Life. When that book is opened and our name is not in it we will be banished from heaven to be tormented in the lake of fire, the pits of hell where there will be weeping and gnashing of teeth forever and ever.

“The Son of Man shall send out His angels, and they will gather out of His kingdom all things that offend and those who practice lawlessness, and will cast them into the furnace of fire.  There will be wailing and gnashing of teeth.”  (Matthew 13:41-42)

“When the Son of Man comes in His glory, and all the holy angels with Him, then He will sit on the throne of His glory.  All the nations will be gathered before Him, and He will separate them one from another, as a shepherd divides his sheep from the goats. And He will set the sheep on His right hand, but the goats on the left… Then He will also say to those on the left hand, Depart from Me, you cursed, into the everlasting fire prepared for the devil and his angels… and these will go away into everlasting punishment, but the righteous into eternal life.”  (Matthew 25:31-33, 41, 46)

“And I saw the dead, small and great, standing before God and books were opened.  And another book was opened, which is the Book of Life… .And anyone not found written in the Book of Life was cast into the lake of fire.”  (Revelation 20:12, 15)

Jesus is the Son of God, the alpha and the omega. The Lamb slain before the foundation of the world. God in eternity past, knew that Adam would sin, so he sent his one and only Son to atone for the sin of all mankind. So Jesus had to become a man, so that he could die as a propitiation for man. When we accept this by faith, we are given eternal life, and we will not perish.