Matthew 28:19-20
Mark 16:15
Acts 1:8
Matthew 10:32
John 20:21
Romans 10:11-15
1 Peter 2.9

Christians are called ambassadors, witnesses, priests.

We are commanded in many instances to follow after Christ, who himself came "to bear witness to the truth" (John 18:37)

Just trust me on this. I know about this stuff. It's commanded. In fact, it's our basic job description of what we're supposed to be doing while we remain in this life.