Believers should not continue to preach to people who have rejected the gospel with scorn and contempt (see Matthew 10:14, Acts 13:44 and following, 18:5-6 and 28:17-28). That certainly doesn't mean that God cannot or will not eventually reach these people, only that we cannot let ourselves get so preoccupied with working to convert one belligerent scoffer that we neglect those who the Spirit has given "ears to hear."

-R