“At the center of the seventh heaven (note there are seven heaves total) is the Populous House (al-bayt al-ma’mur; this is equivalent to the Ka’ba in the higher realms. In the hadiths it is said to be the heavenly sanctuary visited daily by seventy thousand angels, and it corresponds to the Ka’ba in the material dimension. The connection between the Ka’ba and Populous House is uninterrupted, since there are corresponding sanctuaries at the center of each of the other heavens, each being the shadow cast by the one immediately superior to it.
The Ka’ba is the spiritual heart of the terrestrial world, and it is also the projection on the material plane of all the Houses in the higher heavens up to the Populous House, which is the heart of the Universe. The Ka’ba therefore corresponds outwardly to what the heart is inwardly, and this is why we term the Ka’ba the ‘heart of the world’, and the Populous House the ‘heart of the universe.’ Thus the Qur’an verse, Purify My House for those who circle around it, retreat in it, bow and prostrate (22:26), is taken by Imam al-Haddad to refer to the heart with the various influences from the surrounding dimensions revolving around it. Similarly, the physical heart which sends blood and warmth throughout the body is a symbol of the heart of the man of God which radiates lights. The Ka’ba, which radiates the blessings it receives from the higher world throughout the terrestrial world, and the Populous House, which radiates light throughout the universe, are also symbolized by the heart.”
Excerpt from Man and the Universe, by Dr. Badawi