At this point the meaning of his words, “This is my Lord” (6:76), becomes clear: that is, “if, after examining its state and qualities, it proves worthy of divinity, then it is my Lord.” He was, of course, absolutely certain that it possessed not so much as a speck of lordship or godhood; his aim was simply to oblige them with a decisive proof.
“When it set” (6:76)—that is, when it disappeared—“he said, ‘I do not love those that set.’” Anything that alternates between existence and non-existence, or presence and absence, is clearly imperfect; therefore it cannot be a deity.
He then turned to the moon. When he saw it rising he said, “This is my Lord,” but when it set he said, “If my Lord does not guide me, I will surely be among the misguided people” (6:77). In this way—peace and blessings be upon him—he appeared outwardly to agree with them, not in blind imitation but in order to establish a rational proof concerning the alleged divinity of the stars and the moon. Now that they had set, and reason confirmed by revelation had shown the falsity of their godhood, he was in effect saying, “I have yet to settle upon a truly great Lord and God.”
When he saw the sun rising he said, “This is greater”—greater than the stars and the moon—“but if it undergoes what befell them, it is just like them.” And when it set—and all had already conceded that worshipping something subject to setting is the height of falsehood—he pressed the argument and declared, “O my people, I am free of what you associate with God. Indeed, I have turned my face—both outwardly and inwardly—to Him who created the heavens and the earth, ever-inclined to Him alone, and I am not of the polytheists” (6:78).
This is a clear rational demonstration that the Creator of the upper and lower realms alone must be singled out for pure monotheism, and that these spheres, stars, and other bodies are merely created and governed beings lacking any qualities that would entitle them to worship.
They then tried to frighten him with their deities, threatening that they would harm him. This only shows that idol-worshippers entertain corrupt fantasies and worthless notions, imagining that their gods benefit those who worship them and harm those who abandon or denigrate them.