I think the seriousness of evangelism is the main reason it frightens us.  We realize that in talking with someone about Christ, Heaven and hell are at stake.  The eternal destiny of the person is the issue.  And even when we rightly believe that the results of the encounter are in God’s hands and that we are not accountable for the person’s response to the gospel, we still sense a solemn duty to communicate the message faithfully coupled with a holy dread of saying or doing anything that would be a stumbling block to this person’s salvation.  Many Christians feel too unprepared for this kind of challenge, or simply have too little faith and are terrified of entering into such an eternally important situation.