It's being prepared

N. T. Wright nicely illustrates this point [about the city of God being prepared in heaven] with his analogy of a parent telling a child in advance of Christmas that there is “a present kept safe in the cupboard for you.” This does not mean that once Christmas comes, the child has to “go and live in the cupboard in order to enjoy the present there.” Rather, the present will be brought from the cupboard to enrich the life of the child in the day-to-day world.—J. Richard Middleton, A New Heaven and a New Earth, 220