What is the ruling regarding a Christian who was born into their religion and lived a life of good morals, and to whom the Islamic call did da'wah not reach clearly, and will they enter Hellfire, knowing that Allah is Merciful and Forgiving?

Allah is Forgiving and Merciful, but He does not forgive shirk (associating partners with Him), and He accepts no religion other than Islam, which superseded all other religions after the prophethood of the Prophet (peace be upon him). Whoever heard about the Prophet (peace be upon him) and did not believe in his message until he died, his destiny is the Fire, for Allah Almighty says: "Indeed, those who disbelieved among the People of the Scripture and the polytheists will be in the fire of Hell, abiding eternally therein. Those are the worst of creatures." (Quran 98:6). And in a Hadith in Sahih Muslim: "By Him in Whose Hand is the life of Muhammad, there is none among the nations, be he a Jew or a Christian, who hears about me and does not believe in what I have been sent with, but will be among the dwellers of the Fire." As for those who never heard anything about Islam, they will be treated on the Day of Resurrection like the people of the Fatrah (interim period) and will be tested, for Allah Almighty says: "And We would not punish until We had sent a messenger." (Quran 17:15).