Regarding the gospel, there are three types of people:
1) The Christian
2) The uncommitted fence sitter
3) The unbeliever
The Christian is the one who believes the gospel, and has made a commitment of faith in it. The Gospel needs to be preached to this person for the sake of renewing hope, increasing faith, stirring up to do good works (sanctification), and reminding to not trust in any other source.
The uncommitted fence sitter is the one who is convinced that Jesus is the Christ and has come to an intellectual agreement of the gospel, but who has not made a commitment of faith to it. They believe it with their head but subconsciously reject it in their heart, and it’s evident by their refusal to submit to Christ as Lord. The Gospel needs to be preached to this person for the sake of warning of judgment. They need to know that if they refuse to commit their lives to Christ, their knowledge will damn them.
The unbeliever is the one who is not convinced that the Gospel is true, or that Jesus is the Christ. The Gospel needs to be preached to this person so that they would be persuaded that Christ is preeminent above all things, and worthy of our belief and commitment.