God accomplished His eternal purpose in saving man by the death of Christ and His resurrection. Why did God not end the world shortly thereafter? Why has the world dragged on for 2000 years after Jesus victory over sin? One reason is that God is waiting for the harvest, and that takes time for the crop to ripen (Mt 13:30). Another reason I just noticed is that God left the world as an object lesson to those in eternity in what happens when you do not completely purge out the old leaven.
Christianity overcame a large part of the world after it its inauguration. It persisted in Europe against all odds until the beginning of Satan’s little season, and it has since declined to the point of having little practical influence there. Christianity is to continue to decline until Christ could wonder if He would even find faith when He comes again (Lk 18:8). Paul also warns that “evil men will wax worse and worse” (II Tim 3:13) and before Jesus comes a falling away will happen first (II Thes 2:3). The destruction of faith and righteousness on the earth brought about by the fact that God permitted the tares to remain until the harvest shows the utter wisdom of God in completely exterminating wickedness and starting over with the new earth. The new earth will have righteous benevolent dictators over its entire administration and these rulers will never be displaced. Because there will always be righteous administration and because all evil minded persons have been removed, righteousness will endure forever. However, had God not permitted the present age to continue until wickedness inevitably destroyed righteousness, then God’s creatures in eternity would not know the necessity of what God did in rooting out and destroying wickedness at the end of this present age. The possiblity would remain that righteousness would convert all of the wicked and utter destruction would not be required. God’s patience in allowing wickedness to destroy goodness shows His righteousness at the end of the age when He comes and utterly destroys the “Amelekites” whose iniquity has become full.