God makes this promise to Jacob because he is trusting in a Mediator. It is as if he has had a new birth, obtained new consciousness of God, new knowledge.
This ladder is one which many never see though the good news of the gospel has been preached through all the world. It is still in place today but it can only be seen with the eye of faith. When the soul does see it, it is filled with hope at the glorious possibility that presents itself.