By the time Avraham Avinu came upon the scene, the midas ha'din said that all the people in the world did not have the good deeds to reach the minimum level of the World to Come. The World to Come demands a certain minimum level of holiness. Since Adam there has not been anyone with enough to merit the World to Come until Avraham Avinu. Through Avraham, G-d would retain the goal of the World to Come.