Speaking about the affairs of religion must only be done purely for Allāh’s sake. One’s intention must exemplify this in calling to Allāh. The allowance of desires to disturb this pure intention only causes ruin to the hearts of people.
Allāh explained that their splitting only occurred after the knowledge had come to them, and which showed them what they were commanded to do and to avoid. For Allāh does not leave people to stray, except after giving them guidance, until He explains to them what they were commanded to do.
The Roots Of Corruption:
Imām Ibn al-Qayyim (d.751H) – raḥimahullāh – said:
‘‘It is upon the one who speaks in this matter, or any other matter, that He should only do so based upon the knowledge and the truth: and that his objective should be sincerity to Allāh, to His Book, to His Messenger ; and the giving of sincere advice to his Muslim brothers. But if he makes the truth accord with his own whims and desires, then this will corrupt and ruin the hearts, the actions, and the state of affairs. Allāh – the Most High – said:
‘‘And if the truth were to be in accordance with their desires, then indeed the heavens and the Earths – and all that is therein – would be corrupted and ruined.’’
[Sūrah al-Mu’minūn, 23:71]
The Prophet (ṣallallāhu ʿalayhi wa-sallam) said: ‘‘None of you truly believes until he makes desires accord with what I have been sent with.’’ 
So ʿilm (knowledge) and ’adl (justice) are the roots of every good, whereas ẓulm (oppression) and jahl (ignorance) are the roots of every evil. And Allāh – the Most High – sent His Messenger with the Guidance and the Religion of Truth, and he commanded the doing of justice between people and that none of them should follow their whims and desires.
Allāh – the Most High – said:
‘‘So call to Islām and stand firm, and do not follow their whims and desires, but say: ‘‘I believe in whatever has been revealed by Allāh from the Book, and I have been commanded to do justice between you. Allāh is our Lord and your Lord, for us our deeds and for you your deeds. There is no dispute between us and you. Allāh will assemble us all, and to Him is the final return.’’
[Sūrah al-Shūrá, 42:15] 
Allāh – the Most High – said:
‘‘And those who were given the Scripture ( the Jews and the Christians) did not split-up except out of baghee (hatred and envy) between each other, after the knowledge had come to them.’’
[Sūrah Ālī ʿImrān 3:19]
Imām as-Saʿdī (d.1376H) – raḥimahullāh – said:
‘‘This is why Allāh – the Most High ordered the Muslims with ijtimaa’ (collectiveness) in their Religion, and prohibits them from tafarruq (splitting up). he informs them that they must not reject what Allāh revealed tot hem from the Book. Indeed, the People of the Book (i.e. the Jews and Christians) did not split-up until after Allāh had revealed to them the Scripture, in which He ordered them with ijtimaa’ (being unified). However, they did the opposite to what He ordered them with, due to mutual jealousy and hatred. So hatred and jealousy culminated in them having grudges and enmity between one another, then they fell into differing and splitting up. So – O Muslims – beware of doing the likes of this.’’ 
Ibn Taymīyyah (d.728H) – raḥimahullāh – said:
‘‘Allāh explained that their splitting only occurred after the knowledge had come to them, which showed them what they were commanded to do and to avoid. Allāh does not leave people to stray, except after giving them guidance, until He explains to them what they were commanded to do. And He informed that the reason for their tafarruq (splitting) was due to baghee (mutual envy, jealousy, hatred) And baghee occurs due to either falling short of the truth or transgressing the limits. It is due either to abandoning an obligation or doing something prohibited. So know that this is what necessitates tafarruq (splitting).’’ 
A Necessary Jihād:
Shaykh al-Islām Ibn Taymīyyah (d.728H) – raḥimahullāh – said:
‘‘Jihād against the nafs (soul) and its whims and desires is the foundation of jihād against the unbelievers and the hypocrites. Indeed, a person will not have the ability to wage jihād against them, until he wages jihād against his own soul and its whims and desires first.’’ 
Shaykh ʿAbdullāh al-Ghunaymaan – hafiẓahullāh – said:
‘‘It is obligatory upon all those who speak about an affair from the affairs of the Religion that they do so purely for Allāh’s sake, sincerely for the truth. And that they overcome their soul and strive hard against following their whims and desires, not inclining towards worldly matters; such as love of being praised, seeking fame and reputation, gaining a large following and other such matters. So the one who seeks to gain any of this, will gain only the vanities of this world.’’ 
 Tayseerul-Kareemur-Raḥmān (p.701)
 Majmūʿ al-Fatāwá (1/14)
 Da’eef: Related by Ibn Abī ʿĀsim (no.15). It was declared weak by al-Ḥāfiẓ Ibn Rajab in Jāmiʿul-’Uloom wal-Hikam (no.41).
 Madārij al-Sālikīn (93/532-533)
 Related by Ibn al-Qayyim in Dhammul-Hawaa wa Ittibaa’ihi (p. 28)
 Al-Hawá wa Atharuhu fil-Khilāf (p. 20)