God made man in his own image, but did not make him immortal or of the same substance that he possesses. Our Creator is composed of spirit and is eternal. Humans were made, however, out of the ground or organic substance that constitutes the earth. Adam only became a "living being," which is not immortal, when God breathed life into him (Genesis 2:7).
The First Lie
The first lie, in the Garden of Eden, the devil wanted Eve to believe revolves around the concept of an immortal soul! Eve stated she was instructed not to eat from the tree of the knowledge of good and evil or else she would die.
And the woman said to the serpent, "We may freely eat the fruit of the trees of the garden, but of the fruit of the tree which is in the middle of the garden, God has indeed said, 'You shall not eat of it, neither shall you touch it, lest you die.' (Genesis 3:2 - 3, HBFV throughout).
Satan countered that God was lying and that she would not perish (verse 4)! If humans possessed an immortal part of their existence that lives on after death (they always have a conscious existence), then one has to admit the devil was correct!
If the devil's immortal soul teaching that humans never cease to exist upon death were true then God's judgment of Eve would not be righteous!
If humans, however, were not endowed with something that was immortal and conscious after death, then the devil lied to Eve. Her belief, therefore, in his lies constituted a sin and brought upon herself (and Adam) God's righteous judgment.
Here is something else to consider. God's justification for casting Adam and Eve out of the Garden was the following.
And the Lord God said, "Behold, the man has become like one of Us, to decide good and evil; and now, lest he put forth his hand and take also of the tree of life, and eat, and live forever . . . " (Genesis 3:22).
If all humans automatically possess a soul that is immortal (continues their life forever after death) then God's concern makes no sense! His barring them from the Tree of Life would not make a difference since they would already possess something that would keep them alive into the future!
If, however, Adam and Eve did not possess an immortal part of their existence that allowed them to live forever, then God's concern about them acquiring this ability is justified. He did not want his greatest creation, in a rebellious state of mind, to exist forever in unhappiness and misery.
The Bible unquestionably states that the ability to live forever (be immortal) is a gift from God to those who obey him (1Corinthians 15:50 - 55, 2Timothy 1:9 - 10, Romans 6:23, etc.). It is a gift received by those in the first resurrection of the dead. Such a resurrection would be totally unnecessary if humans possessed an immortal soul that went to heaven immediately upon death!
In an instant, in the twinkling of an eye, at the last trumpet (which announces Jesus' return to earth); for the trumpet shall sound, and the dead shall be raised incorruptible, and we (Christians) shall be changed.
For this corruptible must put on incorruptibility, and this mortal must put on immortality. Now when this corruptible shall have put on incorruptibility, and this mortal shall have put on immortality, then shall come to pass the saying that is written: "Death is swallowed up in victory." (1Corinthians 15:52 - 54).
Those in the second resurrection, composed of all those who never had a full chance at salvation, will also be given the opportunity to be immortal (Revelation 20:5, 11 - 13).