The Importance of Muslims Gathering in Assemblies and Other Places, and the Wisdom Behind It (and an explanation of the rule:

The Shaykh: And we say on this occasion: Just as the health of the body from a material and physical health perspective is tied to the health of the heart and its soundness, if the heart is sound in its owner’s body, the body cannot be anything but sound, and the reverse is the reverse: if the heart becomes corrupt, the body becomes ill. Thus says our Prophet (peace and blessings be upon him), reminding us of the obligation to care for rectifying the outward; because this rectification is first a proof of the soundness of the inward, and then there is cooperation between the outward and the inward. As I always and forever say: This hadith gives us a thought or idea that preceded in the minds of some philosophers long ago, and they have not been able to realize it in practice even to this day, which is: what they call perpetual motion.
For example, you press a current button and it continues, from the moment of pressing until Allah wills, without interruption, unless you wish to cut it off, or a car, for example, you move it, it continues without any force, perpetual motion from itself: this is an illusion, but it is a reality regarding the soundness of the inward and the outward. The soundness of the inward affects the soundness of the outward, and the soundness of the outward affects the soundness of the inward. The evidence: Why did the Prophet (peace and blessings be upon him) order gathering in circles of dhikr, as we said earlier, in his saying (peace be upon him): And in the other saying: .
And more than that: His saying (peace be upon him), when the prayer is established: do not say takbir until he orders the straightening of the rows, and he says to them: So, disagreement in the rows leads to disagreement in the hearts, and straightness in the rows leads to straightness in the hearts, their affection, and their unity, and the like. For this reason, he (peace be upon him) cared for rectifying the outward and rectifying the body. And long ago they said: “The soundness of bodies is like the soundness of religions,” so each is connected to the other.
You know that the Prophet (peace and blessings be upon him) orders the Muslim who is afflicted with some illness to seek treatment, where he said (peace and blessings be upon him): , and in another hadith he added: ; so it is obligatory to care for both matters together, and it is not as some ignorant people claim: Oh my brother, the criterion is what is in the hearts. If he is asked why he does not pray? Why does he not perform the obligatory religious duty? He tells you: The criterion is what is in the hearts. I, and praise be to Allah, have not harmed anyone, I have not deceived, I, I, and so on. And this is a liar; Satan has deceived him. He says: I do not deceive anyone, so the first one he deceived is himself; because he disobeyed his Lord. How can he be sound in heart while he does not obey Allah (Mighty and Majestic), at least in what Allah has made obligatory upon him? This is a word before the unity in circles of knowledge; it must be on your minds so that you first follow the commands of the Messenger (peace and blessings be upon him), and so that you remember this reality: that “the soundness of the inward does not suffice for the soundness of the outward, the soundness of bodies does not suffice for the soundness of religions, and the soundness of religions—if the expression of the collective is correct—does not suffice for the soundness of bodies.” Now, what else? What do you have?