Why did Allah Almighty swear by His creation in the Quran, even though He does not need to swear by Himself or by anything of His creation?

Allah Almighty is the Doer of whatsoever He wills, and He is not to be questioned as to what He does. He is entitled to swear by any of His creations, because they are among His signs that indicate His Oneness and His immense power. Sheikh Ibn Uthaymeen clarified that swearing is one of the Arabic linguistic styles used to emphasize matters. It increases the believer's certainty, highlights the greatness of what is sworn by, and indicates the importance of the matter sworn upon. Christians have no right to object to Allah swearing by His creations, for their holy books contain oaths by His creations.