Unity : Pillar of Islam
Unity like tawhid (monotheism), is one of the pillars of Islam. It is unfortunate fact that the issue of unity is perceived as something that is merely encouraged instead of something that is vital to the believer. However, the Qur’an makes unity pinnacle to Islam featuring the same emphasis as it highlights tawhid. So great is the stipulation of a united ummah of believers, that the call for unity precedes the command to worship the One God:
Indeed this ummah (community) of yours is one community (ummah wahidah), and I am your Lord. So worship Me. [Anbiya 21:92]
The above verse clarifies the fact that the devout believers or submitters in God (muslimeen) is one community (ummah wahidah). Therefore, it is an obligatory duty, on Muslims to strive for a single ummah, in the same way that they are obligated on the basis of tawhid to worship one God.
The Almighty had enjoined upon the believers to hold Allah’s rope (i.e. His Book) firmly all together, establish Ad-Deen (i.e. Islam) and not to become divided – double emphasise!
And hold firmly to the rope of Allah all together and do not become divided. And remember the favor of Allah upon you - when you were enemies and He brought your hearts together and you became, by His favor, brothers. And you were on the edge of a pit of the Fire, and He saved you from it. Thus does Allah make clear to you His verses that you may be guided [Aali Imran 3:103].
Allah Almighty had warned the believers in His Book that dividing Ad-Deen into various sects is akin to associating partners with Allah and doing Shirk.
"Turn back in repentance to Him, and fear Him. Establish regular prayers, and be not among those who ascribe partners to God -- those who split up their religion, and become mere sects, each party rejoicing in that which is with itself!" [Ruum 30:31-32]
Which is unforgivable if one were to die upon it.
Indeed, Allah does not forgive association with Him, but He forgives what is less than that for whom He wills. And he who associates others with Allah has certainly fabricated a tremendous sin. [4:48]
Since in doing so one takes humans as the final authority instead of Allah and His Book.
They have taken their scholars and monks as lords besides Allah, and [also] the Messiah, the son of Mary. And they were not commanded except to worship one God; there is no deity except Him. Exalted is He above whatever they associate with Him. [Tawbah 9:31]
The Almighty also made it abundantly clear that sectarianism and division is worse even than idol-worshipping in at least in times of weakness. Recall, how the Prophet Harun (peace be upon him) justified to the Prophet Moses (peace be upon him), worshiping of the calf by the Children of Israel for some time to avoid divisions among them in the longer run [20:88-94].
He said, ‘Son of my mother- let go of my beard and my hair! - I was afraid you would say, “You have caused division among the children of Israel and have not heeded what I said.”’[Ta Ha 20:94]. This was due to his state of weakness: …the people took me as weak and were about to kill me… [Part of A’raf 7:150]. Are the Muslims not in such weakness today?
Allah Almighty had further warned the Believers that if they divide themselves into sects, then Allah’s Prophet (peace be upon him) will have no concern whatsoever with them
Indeed, those who have divided their religion and become sects - you, [O Muhammad], are not [associated] with them in anything. Their affair is only [left] to Allah; then He will inform them about what they used to do. [An’am 6:159].
He further explained with an example that even a holy place like a Masjid that causes division among the believers is unacceptable and worthy of self-destruction
Then there are those who built a mosque––in an attempt to cause harm, disbelief, and disunity among the believers––as an outpost for those who fought God and His Messenger before: they swear, ‘Our intentions were nothing but good,’ but God bears witness that they are liars. [Prophet], never pray in that mosque. You should rather pray in a mosque founded from its first day on consciousness of God: in this mosque there are men who desire to grow in purity- God loves those who seek to purify themselves. Is one who lays his foundation on obtaining righteousness from God and His acceptance better, or one who lays his foundation on the edge of a cliff which is about to crumble, so that it crumbled with him into the fires of Hell God does not guide the wicked people. [Tawbah 9:107-109].
Allah is the one who can truly unite the hearts not worldly factors alone.
And He has united their (i.e. believers) hearts. If you had spent all that is in the earth, you could not have united their hearts, but Allah has united them. Certainly He is All-Mighty, All-Wise. [anfal 8:63]
And remember the favor of Allah upon you - when you were enemies and He brought your hearts together and you became, by His favor, brothers. And you were on the edge of a pit of the Fire, and He saved you from it. Thus does Allah make clear to you His verses that you may be guided [Aali Imran 3:103].
And Allah knows best.
For Younger Readers
God teaches in the Quran, the holy book of Muslims that:
Unity of believers or Muslims is very important
Following God’s guidance from the Quran will lead to unity
Steps should be taken to try and unite
Only God can truly unite the hearts of fellow believers