بسم الله الرحمن الرحيم
The Prophet ( صلى الله عليه وسلم) said:
“Whoever Allah wants good for, He gives him understanding of the religion.”
And understanding of the religion demands acceptance of it, because every person who understands and knows the religion, he accepts it, and loves it.
He, the Exalted, said:
But no, by your Lord, they have not believed, until they make you (O Muhammad صلى الله عليه وسلم) judge in all disputes between them, and find in themselves no resistance against your decisions, and accept (them) with full submission. (An-Nisa 4:65).
So this form of swearing stresses – by use of the statement (No!), and swearing particularly by the Rububiyyah of Allah, the Mighty and Sublime, over His slaves, and it is the mention of Allah’s Rububiyyah over His Messenger – it stresses the negation of faith from Whoever does not abide by these three matters:
The First: Judgement of the Messenger ( صلى الله عليه وسلم) based on His saying: “until they make you judge in all disputes between them” meaning (by you), the Messenger ( صلى الله عليه وسلم).
Whoever seeks judgement from other than Allah and His Messenger, he is not a believer. He is either a disbeliever whose disbelief has brought him out of the religion, or a disbeliever whose disbelief is less than that.
The Second: The chest being open to the judgement; such way that they do not find any resistance in themselves for his decision. They rather find acceptance and openness to what the Prophet ( صلى الله عليه وسلم) decided.
The Third: That they submit, which is stressed; meaning with complete submission.
So beware O Muslim! Of negating faith from yourself. Let us draw an example for this: Two men were arguing about the Shari’ah ruling on an issue. One of them brought evidence from the Sunnah, while the other found difficulty and felt constricted by that. How could he abandon who he follows, so as to follow this Sunnah? This man, without a doubt, has deficient faith, because the believer, in truth, is he who, when he has a text from the Book of Allah and the Sunnah of His Messenger ( صلى الله عليه وسلم) he feels as if he has won the greatest of spoils, and he will be joyful for that, and say: “All praise is due to Allah who guided me to this.” But so-and-so, who is partisan to his opinion, and tries to turn the textual proofs upside down, so that he can make them agree with what he likes, not what Allah and His Messenger intended, then this one is in a tremendous state of danger.
 Reported by Al-Bukhari (71) and Muslim (1037) from Mu’awiyah bin Abi Sufyan, may Allaah be pleased with him.
Source : Al-’Aqidah Al-Wasitiyyah (2 Vol. Set) – Author: Shaykh Muhammad bin Salih Al-’Uthaimin – Publisher: Darussalam Publishers & Distributors. You are encouraged to buy this wonderful book.