In the Name of Allah, peace be upon you.
My question is: What is the ruling of Mushriks or the people of the book who receive the message of Islam but do not join Islam? And what is the ruling of those who do not receive the message of Islam? Similarly, what is the ruling of Christians who admit Allah is One but follow the religion of `Isa (Jesus, peace be upon him)? Will they be among the dwellers of Paradise or the denizens of Hell? Enlighten us, may Allah reward you with good!

Allah, Glorified be He, says: “And whoever seeks a religion other than Islam, it will never be accepted of him, and in the Hereafter he will be one of the losers.” (Al-`Imran, 3:85) The Prophet (peace be upon him) stressed the same ruling by saying that any Jew or Christian who heard about him and did not follow him would be among the denizens of Hell. This is related by Muslim (153) on the authority of Abu Hurairah (may Allah be pleased with him). Anyone who receives the message of Islam and does not enter Islam will not be saved from the punishment of Allah; he will enter the Hell. Allah, Praised be He, says: “…this Qur’an has been revealed to me that I may therewith warn you and whomsoever it may reach.” (Al-An`am, 6:19) The message of Prophet Muhammad (peace be upon him) nullifies all previous messages, for he is the final Messenger and his message prevails over all messages. That is what we believe.
Other rulings are based on this ruling. For example, a Muslim can deal with these people to benefit the Muslims or keep them safe from any harm. This has nothing to do with their belief, for every person with a certain belief thinks he is on the right path. It would not be called belief if he did not think so. This is what makes our belief in Islam firm. As for those who do not receive the message, they take the same ruling as the people who lived in the interval between the prophets. Scholars have two opinions regarding them:
First: As far as the basics of Islam are concerned, they are punished, but this is not so concerning subsidiary matters. Many scholars such as Al-Qarafi adopt this opinion. The author of Maraqi Al-Su`ud says: “The people who lived in the interval between two prophets are not held accountable for subsidiary matters, but scholars differ concerning the basics.” Such people are not required to fulfill subsidiary matters but they are required to follow the principles of Shari`ah; which is to believe in Allah, His angels, books, messengers and the Last Day. But scholars differ in this regard. An example of such a person is someone who lived on an island and did not hear anything of Muhammad’s message. Anyone who did not receive the message takes the same ruling. On the Day of Judgment, he may be resurrected and given the choice, as mentioned in the Hadith related by Ibn Kathir. Thus, the matter is subject to many criteria discussed by scholars (may Allah be merciful to them all).