Qur'an talks about the unity of mankind and disowns those who break this unity.
مِن الَّذِين فَرَّقُواَ
دِينَهُمْ وَكَانُوا شِيَعًا كُلُّ حِزْبٍ بِمَا لَدَيْهِمْ فَرِحُونَ
30:32 Those who split up their religion becoming sects, each sect delighting in whatever beliefs they have. [3:104, 6:160, 23:53, 42:13. Sectarianism is invariably based on taking humans as authorities]
Sectarianism is a result of taking human as authorities and therefore those who indulge in sectarianism are not Muslims .
إِنَّ الَّذِينَ فَرَّقُواْ دِينَهُمْ وَكَانُواْ شِيَعًا لَّسْتَ
مِنْهُمْ فِي شَيْءٍ إِنَّمَا أَمْرُهُمْ إِلَى اللّهِ ثُمَّ يُنَبِّئُهُم بِمَا كَانُواْ يَفْعَلُونَ
6:159 (There is only one straight path.) O Messenger! Those who break the unity of their Deen and become sects, you have nothing to do with them whatsoever. Their case will go to God and He will then tell them what they had been doing.
Only Al-Quran has the power to unite humanity because this book says
كَانَ النَّاسُ أُمَّةًوَاحِدَة and present a workable plan to achieve this objective
مَاكَانَ ِبَشَرٍ َ
ن يُؤْتِيَهُ اللّهُ الْكِتَابَ وَالْحُكْمَ وَالنُّبُوَّةَ ثُمَّ يَقُولَ لِلنَّاسِ كُونُواْ عِبَادًا لِّي مِن دُونِ اللّهِ و
كُونُواْ رَبَّانِيِّينَ بِمَا كُنتُمْ تُعَلِّمُونَ الْكِتَابَ وَبِمَا كُنتُمْ تَدْرُسُونَ
3:79 Never would a human being, whom God has blessed with the scripture, wisdom and Prophethood, thereafter say to people, Be servants of me instead of God. Rather, he would say, Become true devotees of the Lord since you learn and teach the Book and study it as it should be studied.
Al-Quran clearly asks كُونُواْ رَبَّانِيِّينَ . In other words Quran presents a God Centered Deen . Following verse of Quran further strengthen this concept and demolishes the biggest hurdle i.e. personality worship(basis of sectarianism ) which could contaminate this concept.
وَمَا مُحَمَّدٌ إِلاَّ رَسُولٌ قَدْ خَلَتْ مِن قَبْلِهِ الرُّسُلُ أَفَإِن مَّاتَ أَوْ قُتِلَ انْقَلَبْتُمْ عَلَى أَعْقَابِكُمْ وَمَن يَنقَلِبْ عَلَى عَقِبَيْهِ فَلَن يَضُرَّ اللّهَ شَيْئًا وَسَيَجْزِي اللّهُ الشَّاكِرِينَ
3:144 Muhammad is only a Messenger. The Messengers before him have passed on. So, if he died or were slain, would you turn about on your heels? But anyone who turns about his heels, would not, in the least, harm God. And God will soon reward those who remain appreciative (for the guidance).
Quran creates a broad based society on the principle of
صِبْغَةَ اللّهِ
صِبْغَةَ اللّهِ وَمَنْ أَحْسَنُ مِنَ اللّهِ صِبْغَةً وَنَحْنُ لَهُ عَابِدُونَ
2:138 Hue of God! And who can give a better hue (to life) than God? And it is He alone Whom we serve.
[Hue of God = We take our hue from God. Nearest to God are those who have adopted His Sibghah = Hue or Color = His attributes in the human capacity. 83:28. That means adopting the Divine Attributes in our limited human capacity such as:
kindness empathy - creativity mercy - forgiveness turning to people in love and affection (attaining) wisdom knowledge (learning) compassion clemency taking care - peacefulness remaining informed and aware sense of duty - determination justice protecting others generosity unity - self-control leniency - approachability - appreciation moral strength patience - showing light guiding - independence truthfulness maintenance of people and things keeping pledges resolve benefiting others beautiful designing providing listening observing being worthy of trust nobility of character giving sense of responsibility. Interestingly, people can make a self-assessment by this spectrum as to where they stand on the ascending ladder of Tazkiah = Self-actualization or personal development]
This message of صِبْغَةَ اللّهِ present an idea of a society where every person regardless of language, colour, caste, religion etc. strive toward all that is good.
وَلِكُلٍّ وِجْهَةٌ هُوَ مُوَلِّيهَا فَاسْتَبِقُواْ الْخَيْرَاتِ أَيْنَ مَا تَكُونُواْ يَأْتِ بِكُمُ
اللّهُ جَمِيعًا إِنَّ اللّهَ عَلَى كُلِّ شَيْءٍ قَدِيرٌ
2:148 (Mere rituals carry no importance even though people pursue their self-appointed interests.) Each one has a goal toward which he turns. Then strive together toward all that is good. Whatever stand you take, God will bring you all together. Indeed, God is Able to do all things.
and because of this reasons Quran says
هَـذَا بَلاَغٌ لِّلنَّاسِ وَلِيُنذَرُواْ بِهِ وَلِيَعْلَمُواْ أَنَّمَا هُوَ إِلَـهٌ وَاحِدٌ وَلِيَذَّكَّرَ أُوْلُواْ الْأَلْبَابِ 14:52 This is a clear message for all mankind in order that they may be warned thereby, and that they may know that He is One God. Let those endowed with insight take this to heart.
[Danger signs have been posted on the highway of life as the caravan of humanity moves along to the Noble goal of Peace. God is the Sustainer and Cherisher of all humanity and His law is Supreme (1:1, 114:1). Men and women of understanding and discernment, and those of history, anthropology, philosophy, psychology, sociology, and those in positions of authority must pay heed to what their Lord is telling them. 9:31-33, 14:48, 18:48, 48:28, 61:9]