Protection of faith from spiritual corruption

وَقَالَت طَّآئِفَةٌ مِّنْ أَهْلِ ٱلْكِتَـٰبِ ءَامِنُوا۟ بِٱلَّذِىٓ أُنزِلَ عَلَى ٱلَّذِينَ ءَامَنُوا۟ وَجْهَ ٱلنَّهَارِ وَٱكْفُرُوٓا۟ ءَاخِرَهُۥ لَعَلَّهُمْ يَرْجِعُونَ

And a faction of the People of the Scripture say [to each other], "Believe in that which was revealed to the believers at the beginning of the day and reject it at its end that perhaps they will return [i.e., abandon their religion],