This is a much debated issue in Christianity. Today we will look at what the Bible says about it.
Nature shows there is a God
18 “For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who hold the truth in unrighteousness;
19 Because that which may be known of God is manifest in them; for God hath shewed it unto them.
20 For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse:“
God says here that everyone is without excuse because nature clearly shows that God exists.
Those who do not believe in Jesus are already condemned to Hell
John 3:18 “He that believeth on him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God.”
God Promises that those who diligently seek Him will find Him
Matthew 7:7-8 “Ask, and it shall be given you; seek, and ye shall find; knock, and it shall be opened unto you: For every one that asketh receiveth; and he that seeketh findeth; and to him that knocketh it shall be opened.”
Hebrews 11:6 “But without faith it is impossible to please him: for he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him.“
God promises here that if a person diligently seeks God then God will make sure they hear the gospel and have an opportunity to get saved.
I have heard about people in secluded tribes realizing from nature that the true God could not be their idols, but a single all powerful God who created everything. They then began to ask God to reveal Himself to them. Then after many years a missionary came to them and told them the Gospel and they got saved.
God gives everyone a chance to get saved, no one has an excuse. He reveals Himself through nature, and then He makes sure that anyone seeking Him does hear a clear presentation of the Gospel and has an opportunity to get saved.