In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Imaam As-Sadi [may Allaah have mercy upon him] said: It (i.e. Islam) is the religion by way of which Allaah rectified the beliefs, morals, the worldly life and (a person’s) affairs in the afterlife, and by way of which the disunited hearts and the divergent desires unite (upon one correct path).
Commentary: It is a religion of sound rectification, unites the hearts, renounces (vain, evil) desires and deviation from (upright belief, conduct, morals, dealings etc). There is no other affair that can establish sound unity and unite the hearts except this religion. Allaah said: [ إِنَّمَا ٱلۡمُؤۡمِنُونَ إِخۡوَةٌ۬ – The believers are nothing else than brothers (in Islamic religion)]. [Surah Al-Hujuraat. Aayah 10]
It (i.e. Islam) establishes true brotherhood between its adherents. The Prophet [peace and blessings of Allaah be upon him] said, “The parable of the believers in their affection, mercy, and compassion for each other is that of a body. When any limb aches, the whole body reacts with sleeplessness and fever”. [Saheeh Muslim. Number 2586]
The Prophet [peace and blessings of Allaah be upon him] said, “Verily, a believer is like the brick of a building for another believer, each part strengthening the other.” [Saheeh Muslim. Number 2585]
It is a religion that unites hearts that are not in a state of harmony and hearts that harbour enmity towards each other. It stops evil, transgression, hatred, envy, oppression. (1)
Admonition Regarding Sound Unity – By Shaikh Rabee and Shaikh Saaleh Al-Fawzaan:
Obedience to The Messenger Leads to Unity And Bidah Is The Cause of Splitting And Blameworthy Differing
[Ref 1: From 32mins 34secs to 34mins 20secs. https://www.al-badr.net/detail/8LD6UgwQrZ paraphrased excerpt]