Translation:

2. By the Moon as she follow him;

Notes (Tafseer)

6148. The first pair is the glorious sun, the source of our light and physical life, and the moon which follows or acts as second to the sun for illuminating our world. The moon, when she is in the sky with the sun, is pale and inconspicuous; in the sun's absence she shines with reflected light and may metaphorically be called the sun's vicegerent. So with Revelation and the great Prophets who brought it; and the minor Teachers who derive their light reflected, or perhaps doubly reflected, from the original source.