According to astronomers before Copernicus in the sixteenth century, the seven heavens contained the seven planets which revolved around Earth and exerted influences over people and events and even the metals in the Earth's crust. The seven planets of the old cosmology included the Sun (Sol) and the Moon (Luna), which we now don't regard as planets at all. The other five were Mercury, Venus, Mars, Jupiter, and Saturn.

Because he regarded them as 'spiritual symbols of permanent value' which were 'especially worthwhile in our own generation' (this is how he wrote about them when introducing his long 1935 poem, 'The Planets').  What made them so timely for his own generation was that these spiritual symbols were headed by Jupiter (Jove), the kingly, festive, and magnanimous planet.  Lewis thought that his own generation was too often 'Saturnocentric', that is, fixated upon Saturn, the planet of calamity and misfortune and death.  This fixation was no surprise because his own generation had been, as he put it, 'born under Saturn'; many of his contemporaries had been doomed to die in the Great War.  But that was an historical accident, not an eternal truth about the nature of the universe.  The qualities associated with Jupiter were, he thought, a better representation of the heart of spiritual reality.  The hierarchical order of the planets, in which Jupiter was enthroned as king over the other six, was a useful reminder of this heart.  'Of Saturn we know more than enough,' he wrote, 'but who does not need to be reminded of Jove?'