The Quran

فَلِذٰلِكَ فَادعُ ۖ وَاستَقِم كَما أُمِرتَ ۖ وَلا تَتَّبِع أَهواءَهُم ۖ وَقُل آمَنتُ بِما أَنزَلَ اللَّهُ مِن كِتابٍ ۖ وَأُمِرتُ لِأَعدِلَ بَينَكُمُ ۖ اللَّهُ رَبُّنا وَرَبُّكُم ۖ لَنا أَعمالُنا وَلَكُم أَعمالُكُم ۖ لا حُجَّةَ بَينَنا وَبَينَكُمُ ۖ اللَّهُ يَجمَعُ بَينَنا ۖ وَإِلَيهِ المَصيرُ

Muhammad Asad

Because of this, then,¹ summon [all mankind], and pursue the right course, as thou hast been bidden [by God]; and do not follow their likes and dislikes, but say: "I believe in whatever revelation God has bestowed from on high; and I am bidden to bring about equity in your mutual views.² God is our Sustainer as well as your Sustainer. To us shall be accounted our deeds, and to you, your deeds. Let there be no contention between us and you: God will bring us all together - for with Him is all journeys' end."

I.e., because of this breach of the original unity of men's faith in the One God.
Lit., "between you" - i.e., "to induce you to be more tolerant of one another": evidently an allusion to the bitterness which stands in the way of an understanding between the various sects and schools of thought in all revealed religions.