Tafsir of An-Nahl 16:124

{The Sabbath} is a verbal noun derived from "the Jews observed the Sabbath" (sabtat al-yahūd), meaning they venerated their Sabbath.

{The Sabbath was only imposed}—meaning its burden, which was the transformation [into apes]—{upon those who differed concerning it.} Their disagreement regarding it was that they would permit hunting on it at times and forbid it at others. It was their duty to be in unanimous agreement regarding its prohibition after God had decreed upon them abstinence from hunting on it and the necessity of venerating it.

The significance of mentioning this is similar to the significance of the parable of the town that was ungrateful for the blessings of God, and other such examples. It serves as a warning against the wrath of God upon those who disobey, those who oppose His commands, and those who cast off the yoke of His obedience.

If you ask: What is the meaning of "judging between them" if they were all either permitters or prohibitors? I say: It means He will recompense them according to the variation of their actions, in that they were permitters at one time and prohibitors at another.

Another perspective: Moses (peace be upon him) commanded them to set aside one day of the week for worship, and for it to be Friday. They refused him and said, "We want the day on which God finished the creation of the heavens and the earth, which is the Sabbath." However, a small group among them was content with Friday. This was their disagreement regarding the Sabbath: some chose it, while others preferred Friday over it. So, God permitted them the Sabbath and tested them by prohibiting hunting on it. Those who were content with Friday obeyed the command of God and did not hunt on it, while their descendants could not refrain from hunting, so God transformed them, but not the others. He will {judge between them on the Day of Resurrection}, recompensing each of the two groups with what they deserve.

The meaning of "imposing the Sabbath" is that He made it obligatory upon them to venerate it and refrain from hunting on it.

It is recited: Innamā juʿila as-sabtu (The Sabbath was made/imposed—passive voice). And it is recited by ‘Abd Allāh [Ibn Mas‘ūd]: Innā anzalnā as-sabta (We sent down the Sabbath).

{Invite to the way of your Lord with wisdom and good instruction, and argue with them in a way that is best. Indeed, your Lord is most knowing of who has strayed from His way, and He is most knowing of the [rightly] guided.}