"Those to whom We gave the Scripture before it," meaning before the Qur'an, "they are in it," meaning in the Qur'an, "believers," which refers to whoever held fast to the command of Moses and Jesus, and then believed in Muhammad.
﴿الَّذِينَ آتَيْنَاهُمُ الْكِتَابَ مِنْ قَبْلِهِ﴾ مِنْ قَبْلِ الْقُرْآنَ ﴿هُمْ بِهِ﴾ بِالْقُرْآنِ ﴿يُؤمنُونَ﴾ يَعْنِي: مَنْ كَانَ مُسْتَمْسِكًا بِأَمْرِ مُوسَى وَعِيسَى، ثُمَّ آمَنَ بِمُحَمَّدٍ
