Whoever believes means anyone or everyone who hears the gospel of Jesus Christ and makes the choice to believe and follow in His ways. It is such a simple concept and we complicate it.
Having been a pastor I have seen the wide range of reasons why someone couldn't possibly be a Christian because of some issue in the past. I've heard people say, "but they must suffer the consequences their sin." In short many people who call themselves Christian think that non-believers should pay for their sin. No, Jesus did that. He paid for our sin. All we have to do is received it.
John 3:17 spells it out clearly, "God did not send His Son into the world to condemn the world but that the world through Him might be saved."
So if God does not condemn the world why do we? The bottom line here is Christ came for ALL, even non-believers, even if we as believer; don't really like them, even if they make our life difficult, even if they have caused problems in our life.
He came for all.
