﴿ فَٱخْتَلَفَ ٱلْأَحْزَابُ مِنۢ بَيْنِهِمْ ۖ فَوَيْلٌۭ لِّلَّذِينَ ظَلَمُوا۟ مِنْ عَذَابِ يَوْمٍ أَلِيمٍ ﴾

“But factions from among those [who came after Jesus] began to hold divergent views: woe, then, unto those who are bent on evildoing - [woe] for the suffering [that will befall them] on a grie­vous Day!”

وَلِأُبَيِّنَ لَكُم بَعْضَ الَّذِي تَخْتَلِفُونَ فِيهِ (and to explain to you some of those matters in which you differ...43:63) Since Bana Isra'il were drowned in arrogance and obstinacy, they had tampered with the Divine laws. Sayyidna ` Isa (علیہ السلام) disclosed the reality of such distortions. The words 'some matters' are used because some other matters were purely of mundane nature. He might have not felt the need to deal with those differences. (Bayan-ul-Qur an).