In plain words
However long it stays in this earth, gold is a substance that does not spoil. However long it stays in this physical world, the heart is something that does not change. Heart does not mean the physical heart. The spiritual heart. It holds within itself the infinite principle. The Divinity that is in humanness is not of this kind. This liṅga form called hiraṇmaya is in the heart as twelve forms. To these they have long given the name Āditya Brahmas. These Āditya Brahmas are twelve. Because it is held by such Brahmas, the sun, which has taken shape as the twelve months, keeps appearing and passing away each morning in a golden form. But when we look at it in physical science, there is no such thing as beginning and end for it. There is no sunrise and no sunset. When it comes above the equator we think this is day, and when it goes below the equator, night. This night and day are not two suns. The great sage Pippalāda went on teaching such a secret to Śibi
Besides this, to practise the right sādhana for it there are two paths, called feeling and sādhana. One who experiences this praṇava through feeling alone cannot come to know his own Divinity. Even when he knows it, it takes shape as a passing awareness, and afterwards forgetfulness keeps coming over it. One who enters the path called sādhana reaches the divine orb of the sun and from there goes on into the realm of Brahma. You need not think that Brahma means some four-faced Brahmā, some other Brahmā. Brahman means vastness. To attain the feeling of Brahman means nothing other than to attain a vast feeling. The idea in today's science is like this: a finer particle within the atom, a finer particle within that particle; in this way one thing keeps growing smaller than another. But spirituality is not like that. Mahato mahīyān, mahato mahīyān: it keeps on expanding. This is the nature of Brahman. Brahman means vastness itself. That the moon means Manas, that the sun means the light of the eye. Only one who recognises such Vedāntic import, the meaning of the words, can grasp the right meaning in this spirituality.
What is this liṅga? Is it in this physical body? Vedānta called this very thing aṅguṣṭhamātram. That is, we think of it as the physical heart.