People die because of what is called the “original sin”—the disobedience of Adam and Eve in the Garden of Eden. God had warned the first couple that transgressing His law would result in their death (Genesis 2:17), and that is what happened. “The wages of sin is death” (Romans 6:23a).
Adam and Eve were meant to dwell with God forever, so they probably did not even know what it meant to “die.” Unfortunately, sin had at some time in eternity past invaded the heavenly realm of angels, and Satan tempted Eve, and she fell into sin. Eve gave the fruit to her husband, and he followed her into sin. That sin brought death into the world, as mankind separated themselves from the Source of Life.
Since that time, every human produced by a woman with the aid of a man has produced sinful offspring. This sin nature brings with it death. “Sin entered the world through one man, and death through sin, and in this way death came to all people, because all sinned” (Romans 5:12).
Genesis 3 describes the curse that God pronounced upon the world. The curse included these words to Adam: “You [will] return to the ground, since from it you were taken; for dust you are and to dust you will return” (Genesis 3:19). Physical death of the body is what God spoke of here. Physical death did not occur immediately for Adam and Eve, but, because of their sin, innocent animals did die (Genesis 3:21).
The other type of death that Adam and Eve’s sin brought was spiritual death—their spirits were separated from God’s Spirit; their fellowship was broken. This spiritual death occurred immediately after they partook of the forbidden fruit and were fearful and ashamed (Genesis 3:10). Spiritual death, like physical death, was passed on to their descendants (Ephesians 2:1).
Ever since Adam, the human race has labored under “the law of sin and death” (Romans 8:2). God in His goodness sent His Son to abolish the law of sin and death and establish “the law of the Spirit who gives life” (Romans 8:2). First Corinthians 15:20–26 states, “Christ has indeed been raised from the dead, the firstfruits of those who have fallen asleep. For since death came through a man, the resurrection of the dead comes also through a man. For as in Adam all die, so in Christ all will be made alive.… The last enemy to be destroyed is death.”
 Got Questions Ministries. (2010). Got Questions? Bible Questions Answered. Bellingham, WA: Logos Bible Software.