Word by Word Analysis

وَلَن تَرْضَىٰ عَنكَ ٱلْيَهُودُ وَلَا ٱلنَّصَـٰرَىٰ حَتَّىٰ تَتَّبِعَ مِلَّتَهُمْ ۗ قُلْ إِنَّ هُدَى ٱللَّهِ هُوَ ٱلْهُدَىٰ ۗ وَلَئِنِ ٱتَّبَعْتَ أَهْوَآءَهُم بَعْدَ ٱلَّذِى جَآءَكَ مِنَ ٱلْعِلْمِ ۙ مَا لَكَ مِنَ ٱللَّهِ مِن وَلِىٍّ وَلَا نَصِيرٍ 120

And never will the Jews and the Christians approve of you until you follow their religion. Say, "Indeed, the guidance of Allāh is the [only] guidance." If you were to follow their desires after what has come to you of knowledge, you would have against Allāh no protector or helper.