He, glorified be He, could have made it stationary and fixed in that state. Then He created the sun and established it as a guide to that shade. The shade follows its movement, increasing and decreasing, extending and contracting with it. It thus follows the sun as what is indicated follows its indicator.

There is another interpretation: what is meant may be the withdrawal of the shade when the Hour comes, through the removal of its causes—the bodies that cast shadows. On this reading, He would have described its disappearance through the removal of its causes, just as He described its creation through the creation of its causes.

His words, “We drew it back to Us,” seem to suggest this.

His words, “an easy, gradual drawing back,” resemble His words: “That is a gathering easy for Us.” [50:44]

The past tense in “We drew it back” does not rule this out, as in His words, “The command of Allah has come.” [16:1] The first interpretation, however, is the intended meaning of the verse.

[Surah al-Furqān (25): verse 55]
“And they worship besides Allah what can neither benefit nor harm them. Yet the disbeliever is ever an ally against his Lord.” (55)

This is among the Quran’s most subtle expressions and noblest meanings: the believer always sides with Allah against his own self, his desires, his devil, and his Lord’s enemy. This is what it means for him to belong to Allah’s party, His army, and His allies. He sides with Allah against his enemies, both within himself and outside him, fighting them, opposing them, and hating them for His sake, glorified be He. This is like a king’s close attendants joining him in fighting his enemies, while those far removed from him remain unoccupied with this and unconcerned about it.

The disbeliever, by contrast, sides with his devil, his own self, and his desires against his Lord.

The explanations of the early generations revolve around this meaning. Ibn Abī Hātim related from ‘Atā’ ibn Dīnār, from Sa‘īd ibn Jubayr, who said: “A helper to Satan against his Lord through enmity and associating partners with Him.”

Layth and Mujāhid said: “He supports Satan in disobedience to Allah, helping him in it.” Zayd ibn Salm said: “‘An ally’ means one who gives allegiance.”

The meaning is that he allies himself with Allah’s enemy in disobeying Him and associating partners with Him, and thus stands with His enemy