Why does God, may He be exalted, swear by some of His creation in the Qur’an?
Question

The Christians think that God, may He be exalted, does not need to swear by Himself or by any of His creation, but in the Qur’an it says that He swore by some of His creation. Can you explain this point?
Praise be to Allah.Firstly:
We must understand that Allah, may He be exalted, does whatever He wills; He is not to be asked about what He does whereas they will be asked. The human does not have the right to ask the Lord about what He does and why He did it? Rather what is required of him is to do what Allah commands him to do. When Iblees objected to his Lord, when He commanded him to prostrate to Adam (peace be upon him), and said: {Should I prostrate to one You created from clay?} [al-Isra’ 17:61], Allah cast him out from His mercy.
Al-Qurtubi (may Allah have mercy on him) said:
Allah may swear by whatever He wills of His creation, both animate and inanimate, even if the wisdom behind that is not known." (Al-Jaami‘ li Ahkaam al-Qur’an 19/237).
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:
This is one of the actions of Allah, and Allah is not to be questioned about what He does. He, may He be glorified, may swear by whatever He wills of His creation, and He is the one Who questions and is not to be questioned, the one who judges and is not to be judged." (Majmoo‘ Fataawa wa Rasaa’il Ibn ‘Uthaymeen 10/797).
Secondly:
These things by which Allah swears are some of His signs, evidence of His oneness and proof of His might and ability to resurrect the dead. His swearing by them highlights His glory and alerts people to what they have of proofs of His oneness; they are signs that point to the greatness of His might and His complete control. This is by way of establishing proof so as to leave no excuse for people, as He swore to them by these great created things so that they will pay attention to the importance of the matter attested to and the fact that what He swears by is connected to what He testifies to.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
Allah swears by some of His creation because they are His signs and creation, so they are indicative of His Lordship, divinity, oneness, knowledge, might, will, mercy, wisdom, greatness and glory. He, may He be glorified, swears by them because swearing by them involves affirming His greatness, may He be glorified.  But we should not swear by them, as is indicated by the religious texts and scholarly consensus." (Majmoo‘ al-Fataawa  1/290).
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:
The fact that Allah swears by these signs is proof of His greatness, perfect might and wisdom. Thus swearing by these things, which indicates that these things are of great significance and importance, implies praise of Allah, may He be glorified and exalted, because these things point to His greatness. As for us, we should not swear by anything except Allah and His Attributes, because we are forbidden to do so." (Majmoo‘ Fataawa wa Rasaa’il Ibn ‘Uthaymeen  10/798).
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) explained the wisdom behind Allah’s swearing by His creation, as he said:
If it is asked: what is the point of His swearing oaths even though He speaks the truth and there is no need for an oath, because if swearing an oath is for people who believe in Him and believe in His word, there is no need for it, and if it is for people who do not believe in Him there is no point in it, for Allah, may He be exalted, says (interpretation of the meaning): {And if you brought to those who were given the Scripture every sign, they would not follow your qiblah} [al-Baqarah 2:145]?
My response is: The benefits of {Allah’s] swearing an oath are many:
1. This is the style of the Arabic language, to affirm things with oaths, even if they are known to everyone or unknown to those to whom the oath is addressed, and the Qur’an was revealed in a plain Arabic tongue.
2. The believer increases thereby in certain faith in Allah’s words, and there is nothing wrong with having one more affirmation that will increase a person’s certainty. Allah, may He be exalted, tells us that Ibraaheem said (interpretation of the meaning): {“My Lord, show me how You give life to the dead.” [ Allah] said, “Have you not believed?” He said, “Yes, but [I ask] only that my heart may be satisfied”} [al-Baqarah 2:260].
3. Allah swears by great things which are indicative of His perfect might, greatness and knowledge. It is as if, by means of what he swears by, He is establishing proof for the soundness of what He is attesting to by means of the greatness of the things by which He swears.
4. It highlights the great status of the things by which He swears, because He only swears by great things. In this case, the swearing of the oath is not for the purpose of affirmation: rather it is to refer to the signs by which He swears in order to highlight their importance and draw attention to their greatness.
5. It draws attention to the thing by which the oath is sworn, to indicate that it is worth paying attention to it and affirming it. End quote.
Majmoo‘ Fataawa wa Rasaa’il Ibn ‘Uthaymeen (10/612-613).
Secondly:
With regard to the Christians’ claim that their religion does not see any need for oaths, and their seeking to confuse the Muslims thereby, we have noted above that to Allah belongs the command before and after (ar-Room 30:4), and He, may He be glorified, may swear by whatever He wills and do whatever He wills: {He is not questioned about what He does, but they will be questioned} [al-Anbiya’ 21:23].
Moreover, the Christians have no right to object to this and speak about something that is also seen in their religion and in their Bible. It is not true that in their scripture, God does not swear by any of His creation.
For example, the Bible says:
The Lord has sworn by the pride of Jacob: “Surely I will never forget any of their deeds
(Amos 8:7 – Revised Standard Version).
In the famous King James Version of the Bible, the same verse is translated as: “The Lord hath sworn by the excellency of Jacob, Surely I will never forget any of their works.”
Moreover, the God of the Bible swears by a thief, a cheat and an adulterer! Because Jacob stole the birthright (prophethood) from his brother Esau (Genesis 27) and tricked his maternal uncle Laban with regard to the sheep (Genesis 30:32-43). He was also married to two women, Rachel and Leah (who were sisters!), and he had relations with two slave woman who belonged to his wives Rachel and Leah, namely Bilhah and Zilpah (Genesis 30:4 and 30:9-10). Thus he is regarded as an adulterer according to Christian standards!
We Muslims respect the noble Prophet of Allah Jacob (Ya‘qoob – peace be upon him), and do not believe the fabrications of the fabricators and the lies of the liars. Rather we say to these people:
One of you sees the speck in his brother’s eye, and does not see the plank in his own eye!
 
“Do not judge, or you too will be judged. 
2 For in the same way you judge others, you will be judged, and with the measure you use, it will be measured to you.
 
 
3 “Why do you look at the speck of sawdust in your brother’s eye and pay no attention to the plank in your own eye? 4 How can you say to your brother, ‘Let me take the speck out of your eye,’ when all the time there is a plank in your own eye? 5 You hypocrite, first take the plank out of your own eye, and then you will see clearly to remove the speck from your brother’s eye.
Matthew 7:1-4.
That applies if there is a speck in your brother’s eye, so how about if the speck is in your own eye, so you thought, because it was in your own eye all along, that there was a speck in everything you see?!
Whoever tastes bitterness in his mouth due to sickness will taste bitterness even in fresh, sweet water.
And Allah knows best.