Isaiah 65:20
There shall be no more thence an infant of days, nor an old man that hath not filled his days: for the child shall die an hundred years old; but the sinner being an hundred years old shall be accursed. There shall be no more thence an infant of days, nor an old man that hath not filled his days: for the child shall die an hundred years old; but the sinner being an hundred years old shall be accursed.
The verse belongs to the picture of the Jerusalem that God creates and makes glad, a place with no more weeping or crying. It describes the new earth, the earth restored from the effects of the curse to its condition before the fall, including peace among the animals. It does not describe life on the present mortal earth under the curse, and it does not teach that all people in the fallen world become holy.
The statement that a child will die a hundred years old means that life will be so long that one who dies at a hundred is still regarded as a child, and a hundred years is not a full lifespan. It illustrates the same scale of longevity as before the flood, when people lived many hundreds of years, nearly one thousand years, so that a hundred years old was still youth. Before the flood people lived that long with sound minds in sound bodies, and with strength of intellect and mental and physical power to which the present feeble, degenerate generation bears no comparison. They possessed skill and art in ancient arts now lost, and having nearly one thousand years in which to acquire knowledge, they came upon the stage of action from sixty to one hundred years old, about the time those who now live the longest have acted their part in their short lifetime and passed off the stage.
The statement about the sinner means that a sinner who lives to a hundred years old will be accursed. The verse describes the kingdom of Christ, whose government is like no earthly government but is a representation of the characters of those who compose the kingdom. It is a court where holy love presides and whose offices and work are graced by charity, pity and lovingkindness, where servants find happiness and satisfaction in reflecting the love and tender compassion of the divine nature to all with whom they associate.
The chapter containing the verse speaks in a most decided manner calling for reformation through the congregation of Israel, to stop complaining and evil working and to put away the evil of works. It calls them to come nigh, repent and be converted because present ways are not accepted of God, so that the Lord appears for the conviction and conversion of souls. This speaking is understood when the reformation described in Isaiah 60 and Isaiah 61 comes to the people of God.