What is the ruling concerning those who followed a religion other than that of the Messiah during the time of his advent, and are they considered among the people of Hellfire, and what was the religion they should have followed at that time?

Divine messages agree on the origin of religion, which is the monotheistic worship of Allah, while differing in practical laws. The fact that messengers before Prophet Muhammad, peace and blessings be upon him, were sent specifically to their own peoples does not mean they differed in the origin of religion. Rather, following the branches of their Sharia (law) was exclusive to their own peoples. As for their agreement on the origin of religion, it is general and binding upon all people. The sending of a prophet specifically to his people means that their invitation is binding and their response is obligatory, and it does not prevent the invitation or adherence of others. Monotheism may be general in the case of some prophets, even if the branches of their Sharia were not general. The Arabs and others, even if they were not bound by the branches of the Sharia of Moses and Jesus, are bound by the origin of religion, which is the religion of all prophets.