What should people have followed to enter Paradise, before the advent of Prophet Muhammad (peace be upon him) and after the distortion of Islam brought by Jesus (peace be upon him)?

Allah Almighty looked upon the people of the earth before the advent of the Prophet Muhammad, peace and blessings be upon him, and loathed them, both Arabs and non-Arabs, except for remnants among the People of the Book. Those who did not deserve Allah's loathing and wrath were those who adhered to their true religion, the religion of monotheism, and did not distort it. At that time, it was incumbent upon all people to follow their path to be saved from Allah's loathing and wrath. This includes those who adhered to the religion of Christ and did not distort it.