The Prophets and Messengers (peace be upon them) unanimously affirmed that only those who embrace Islam, believe in Allah without associating partners with Him, and acknowledge all His Prophets and Messengers will find salvation in the Hereafter. Consequently, individuals who followed the teachings of Moses during his era were considered Muslims and devout believers. However, with the advent of Jesus, it became incumbent upon Moses's followers to follow Jesus. Those who believed in Jesus were regarded as righteous Muslims, while those who rejected his Message and clung exclusively to Moses's religion were deemed disbelievers for rejecting a Messenger sent by Allah. Now, with the sending of Muhammad, every individual must believe in him. It is Allah Who sent Moses, Jesus, and the last Messenger, Muhammad (peace be upon them all). Therefore, those who reject Prophet Muhammad's message and adhere to the doctrines of Moses or Jesus are considered disbelievers.
Merely claiming to respect Muslims or giving charity to the poor is insufficient for salvation. True salvation requires belief in Allah, His Scriptures, Messengers, and the Last Day, for one's deeds to be accepted by Allah. The gravest sins include polytheism, disbelief in Allah, rejection of the revealed Scriptures, and denial of the Prophethood of the final Messenger, Muhammad (peace be upon him). Jews and Christians, who have been informed about the mission of Prophet Muhammad (peace be upon him), but choose not to believe in him and reject Islam, will face eternal perdition in Hell, as promised by Allah,{إِنَّ الَّذِينَ كَفَرُوا مِنْ أَهْلِ الْكِتَابِ وَالْمُشْرِكِينَ فِي نَارِ جَهَنَّمَ خَالِدِينَ فِيهَا ۚ أُولَـٰئِكَ هُمْ شَرُّ الْبَرِيَّةِ}“Those who disbelieve from the People of the Book and the polytheists will be in the fire of Hell, abiding therein forever. It is they who are the worst of creatures.”
[98: 6].
Given that the final message has been revealed by Allah to humanity, those who are aware of Islam and have heard about the last and final Messenger, Muhammad (peace be upon him), are obligated to believe in him, follow his religion, and adhere to his teachings. Nonetheless, those who hear about this final divine message but reject it will find their deeds unacceptable by Allah, and they will face punishment in the Hereafter. The evidence for that is Allah’s saying,﴿وَمَن یَبۡتَغِ غَیۡرَ ٱلۡإِسۡلَـٰمِ دِینࣰا فَلَن یُقۡبَلَ مِنۡهُ وَهُوَ فِی ٱلۡـَٔاخِرَةِ مِنَ ٱلۡخَـٰسِرِینَ﴾“Anyone who seeks a religion other than Islam, never will it be accepted from him; and in the Hereafter he will be among the losers.”
[3: 85].
Allah Almighty also says,(قُلْ يَا أَهْلَ الْكِتَابِ تَعَالَوْا إِلَىٰ كَلِمَةٍ سَوَاءٍ بَيْنَنَا وَبَيْنَكُمْ أَلَّا نَعْبُدَ إِلَّا اللَّهَ وَلَا نُشْرِكَ بِهِ شَيْئًا وَلَا يَتَّخِذَ بَعْضُنَا بَعْضًا أَرْبَابًا مِّن دُونِ اللَّهِ ۚ فَإِن تَوَلَّوْا فَقُولُوا اشْهَدُوا بِأَنَّا مُسْلِمُونَ)“Say, “O people of the Book, come to a common term between us and you, that we worship none but Allah and associate no partners with Him, and that we do not take one another as lords besides Allah.” But if they turn away, say, “Bear witness that we are Muslims [submitting to Allah].’”[3: 64].