After that, it was said that 'We have subjugated the sun and the moon for you' as they both keep moving, always in the same state. The word: دَائِبَيْنِ ۖ (da'ibayn) is a derivation from دَأب da'b which means habit. The sense is that moving at all times and under all conditions has been made the habit of these two planets as it never happens contrary to that. The expression: سَخَّرَ لَكُمُ ' (sakhkhara lakum: He subjugated for you) does not mean that they should be moving on your command. Had the sun and the moon been subjugated for human beings in a way that they would be moving under human command, then, there would have been mutual differences among them with the result that one of them would demand that the sun should better rise today two hours later than usual because he had too much work to do in the night. And the other would want to have it rise two hours earlier than usual because he had too many daytime jobs at hand. Therefore, the great Lord did, in a way, subjugate the sun and the moon for human beings, but He did so in the sense that they have been subjugated to serve human beings all the time and under all conditions under a wise Divine arrangement - not that their rising and setting and their speed become subservient to human pleasure.
Similarly, the statement that We have subjugated the night and the day for you' also means that both of them have been put in the service of human beings to provide convenience and comfort.