But what about people who lived before the Bible was written, what about people who have never heard the Word of God from the Bible?
These are valid questions. Actually there are two external witnesses to God’s existence outside of the Bible and they are Nature itself (all that we can see in our world and universe) and the conscience that every person inherently has within, the basic knowing of right and wrong.
Romans 1:20 (NIV) reads: “For since the creation of the world God’s invisible qualities—his eternal power and divine nature—have been clearly seen, being understood from what has been made, so that people are without excuse.”
And Romans 2:13-16 (NIV) which reads:
13 For it is not those who hear the law who are righteous in God’s sight, but it is those who obey the law who will be declared righteous. 14 (Indeed, when Gentiles, who do not have the law, do by nature things required by the law, they are a law for themselves, even though they do not have the law. 15 They show that the requirements of the law are written on their hearts, their consciences also bearing witness, and their thoughts sometimes accusing them and at other times even defending them.) 16 This will take place on the day when God judges people’s secrets through Jesus Christ, as my gospel declares.
I ran across an excellent PDF on this subject authored by PETER GUIRGUIS who runs the http://notashamedofthegospel.com/ website. If you have a few minutes, take a look at it, it is very well done. Just click on the link below to view it or you can download it yourself from Peter’s website.