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.