A lot of good Scripture has been cited, but not yet that which addresses the obvious question to ask at this point: “What is GRFS for those who have never heard of Jesus?” (which includes everyone living B.C. and millions of people who have lived A.D.)
God’s plan of salvation is the same for everyone since Jesus’s death on the cross. God is no respecter of person. He doesn’t require one thing of me and something else of you. We have the answer to your question in Acts 8. The Ethiopian eunuch had never heard of Jesus. He was reading the Old Testament and happened to be reading a prophecy about Jesus. The eunuch had no idea who the writer was talking about. That’s why he asked Phillip the question, “Who is the writer talking about? Himself or some one else? Phillip began with that scripture and “PREACHED JESUS” to him. We are not told Phillip’s exact words but whatever he preached it included the fact that Jesus was the Son of God, because later The eunuch made the confession that he believed Jesus was the Son of God. And we know Phillip had to have preached baptism, and he must have taught how important baptism was because as soon as the eunuch saw some water, he wanted to be baptized. That’s how people after Jesus died on the cross were saved. The blood that Jesus shed on the cross not only teaches forward to save everyone on our side of the cross, but it also reaches backward to save all those who lived before His death on the cross. We all know that the law changed when Jesus died on the cross. Col. 2:14, Hebrews 9:16-17. The people before the “cross” were saved by keeping the law that they were living under; which for the Jews was the law given by Moses at Mt. Sinai. They were not responsible for anything under the new law of faith given by Christ in the New Testament if they died before that law came into effect. 2 Tim. 2:15 we must know how to “RIGHTLY DIVIDE THE WORD OF GOD.”