Then comes the end, when he delivers the kingdom to God the Father after destroying every rule and every authority and power.  For he must reign until he has put all his enemies under his feet.  The last enemy to be destroyed is death.  For " God has put all things in subjection under his feet." But when it says, "all things are put in subjection," it is plain that he is excepted who put all things in subjection under him.  When all things are subjected to him, then the Son himself will also be subjected to him who put all things in subjection under him, that God may be all in all. 1 Cor. 15:24-28 (ESV)
The last enemy to be destroyed is death. Christ has conquered death, and ruined its power over us by forgiving our sins with His death on the cross. On the last day when Christ raises the dead, death will be destroyed, and the kingdom will be delivered to the Father, we will be given to God. For we are the kingdom of Christ. Christ reigns over us with grace and forgiveness of sins, until that day when sin will no longer be. For as long as we live in this world there will be sin in our lives and we cannot approach the Father outside of Christ. But when the kingdom is delivered to the Father, we will no longer have sin, and no need to fear the wrath of God, as even now we need not fear the wrath of God, because Christ forgives our sins.