Death can be defined as separation. Physical death is the separation of the spirit and the soul from the body; spiritual death, is the separation of a person from God; ( as in the case of people who have not accepted and received Jesus Christ as their Savior ) and the second death is eternal separation from God, in the Lake of Fire, without no hope.

By his death, burial, and resurrection, Jesus Christ defeated death, the grave, and hell, for all of humanity. His victory has become our victory, delivering us from the fear of death. ( This is not automatically applied to the human race, it is only to those who have receive Jesus as their Savior).

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Jesus Defeated Death

HEBREWS 2:14-15   Forasmuch then as the children are partakers of flesh and blood,
he also himself likewise took part of the same; that through death he might destroy him
  that had the power of death, that is, the devil;
  Vs.15   And deliver them who through fear of death were all their lifetime subject to
  bondage.

REVELATION 1:18   I am he that liveth, and was dead; and behold, I am alive for
  evermore, Amen; and have the keys of hell and death.

Physical Death

GENESIS 3:19   In the sweat of thy face, shalt thou eat thy bread, till thou return to the
  ground, for out of it thou was taken, for dust thou are and unto dust thou shall return.

HEBREWS 9:27   It is appointed unto men once to die, but after this the judgment.

2 CORINTHIANS 5:8   We are confident I say and willing rather to be absent from the
  body and to be present with the Lord.

Spiritual Death

EPHESIANS 2:1   You hath he quickened, who were dead in trespasses and sins.

EPHESIANS 4:18   Having the understanding darkened, being alienated from the life of
  God through ignorance that is in them, because of the blindness of their hearts.

2nd Death

REVELATION 20:14   And death and hell were cast into the Lake of Fire. This is the
  2nd. death. ( see also John 8:24 )

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