[other] ways for they will separate you from His way.” [1
This divine command emphatically makes it binding on all Muslims to be united as one community of believers; thus, all forms of schism and sectarianism are un-Islamic.
The Prophet’s companions and following generations adhered very closely to the path of God, and thus He protected them from separating in this manner. But with later generations certain factors led to the emergence of divisions and divergence, among them: increasing concern with worldly affairs, the influence of non-Muslim cultures, and political rivalries. Initially, some small groups split off from the path adhered to by the majority of Muslims. They introduced innovations into the religion and followed opinions differing from the original teachings of the Prophet.
These schisms were rejected and opposed by the recognized scholars of Islam and the majority of Muslims, which meant that initially they were contained and that their influence did not become widespread during the major part of Islamic history. The majority of Muslims remained on the Sunni path, and whenever forms of deviation emerged among them, the pious scholars always hastened to oppose them and point out their error.
Prophet Muhammad foretold that such divergences would emerge. He warned against schism and instructed Muslims to remain within the main body of Islam.
Nevertheless, over the centuries a number of people have deviated and corrupted their religion, forming sects that claim to belong to Islam but whose stated beliefs are clearly contrary to it. Some have distorted the concept of God and attributed to Him what is unfitting or incompatible with His divine status – claiming, for example, that everything in existence is God or that He is incarnate or present within His creation, while the Qur’an states that He is superior to His creation and distinct from it. And some have been misguided regarding various major tenets of Islam to the degree that they no longer submit to God and obey Him, while others have innovated and changed some of the prescribed forms of worship.
Those sects which deviated from mainstream Islam are not the same as the schools of Islamic jurisprudence which developed within it and are based on the immutable principles of the faith. These eminent schools of thought have provided a vision of the highest degree of scholarship for
Islamic legislation and serve to complement one another. Differences and disagreements within the framework of Islam do not become matters of partisanship and intolerance except among the extremely ignorant.
Islam recognizes the individuality of human beings and that not all diversity of opinion and difference in analysis is negative. However, the kind of dissension that leads to divisions and sectarianism has been denounced in the Qur’an:
“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.” 
Although Muslims now appear to be divided more than ever before, the number of divisions in Islam remain fewer than in other religions. One can still find many Islamic associations calling people to truth, proclaiming God’s original message, and naming against that which is contrary to it. Salvation does not depend on affiliation with any specific group but rather on true faith proven by obedience to God and upright conduct in the manner revealed by Him.
1 6:153 The subtitle change in the verse from first to third person expresses the progressive process of distancing oneself from God’s path.
2 A Sunni is one who takes his religion from the Qur’an and Sunnah, i.e., the authentically narrated teachings of Prophet Muhammad as practiced by him and his righteous followers.
3 The Hanafi, Maliki, Shafi’i and Hanbali schools and a few others less known. 23 6:159