This question is for people who believe the bible is 100 percent true and that missionary work is very important

Romans 2:12-16 speaks to this:

"For as many as have sinned without law shall also perish without law: and as many as have sinned in the law shall be judged by the law; (For not the hearers of the law are just before God, but the doers of the law shall be justified. For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves: Which shew the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another;) In the day when God shall judge the secrets of men by Jesus Christ according to my gospel."

First thing to note is that your question is a moral question. You are questioning the morality of God. However, since you are an unbeliever who has no final authority, you have no objective standard for truth, so you have no basis for your moral questioning or claims. Your world is a relativistic, subjective and solipsistic one.

Secondly, everyone knows that God exists through nature and conscience. No matter how much anyone has suppressed the knowledge of God.

Before Christ died, we can see that everyone in the Old Testament was still saved by faith. One out of many examples was Abraham, where it says in Genesis 15:6, "And he believed in the LORD; and he counted it to him for righteousness." They didn't have the full picture because they saw through a glass, darkly, but men were always saved by faith in the one true God of the Bible. Christ's sacrifice applied to people before Christ because it is retroactive, even though it hasn't happened in time yet. Remember, God is outside of time.

God has missionaries all around the world sharing the gospel. For the ones that never hear it and end up in Hell, well, I believe that even if they had heard it they wouldn't have accepted it anyway, and God knows this, so that is why they never hear it. God will get true seekers the truth about Christ so that they can get saved. God is not willing that any should perish, but that all should come to repentance.