Then he should say: 'As large as this ether (all space) is, so large is that ether within the heart. Both heaven and earth are contained within it, both fire and air, both sun and moon, both lightning and stars; and whatever there is of him (the Self) here in the world, and whatever is not (i. e. whatever has been or will be), all that is contained within it.

In plain words: The answer is that the space inside the heart is as big as all of space outside. Heaven and earth, fire and air, sun and moon, lightning and stars, and everything that is, was or will be are all held within it.