God is so extremely great that if you grow up as a child of God, it will take all of eternity to get there. Focus on being a child of God so that you can start to grow.
But not great enough to create a universe instantly...
Great doesn't have anything to do with instant.
Some people might paint a beautiful painting instantly if they could. But they wouldn't do it all the time, because part of the joy in painting is the painting of the painting.
