وَلا تُجَادِلُوا أَهْلَ الْكِتَابِ إِلا بِالَّتِي هِيَ أَحْسَنُ إِلا الَّذِينَ ظَلَمُوا مِنْهُمْ وَقُولُوا آمَنَّا بِالَّذِي أُنْـزِلَ إِلَيْنَا وَأُنْـزِلَ إِلَيْكُمْ وَإِلَهُنَا وَإِلَهُكُمْ وَاحِدٌ وَنَحْنُ لَهُ مُسْلِمُونَ
This follows from 29/44-45. 29/44 talks about the evolution of the heavens and the earth symbolising a social evolution with the truth and 29/45 talks about reflecting upon the current set of commands (al-kitab) given to the Reader with which he constructs his existence (tasna3oon).
20/46 tells us not to dispute with the people connected to this set of commands except what is more beautiful (this is a criteria for interpretation in fact) and even that for those who have oppressed. Our philosophy should be that we believe in what in sent down to us and what is sent down to them (two different understandings) and that god is one. Following this, the measure of action is that we are instigators of wholeness and soundness.