"By this all will know that you are My disciples, if you have love for one another." --John 13:35
This is the evidence of a true believer and the evidence that will convince the unbeliever. It is not our apologetics but our love for each other.
We are also called to love all saints, not just those in our denomination or who look like us or use the same translation. This doesn't mean we compromise but Christ wants His kids to treat each other with love and respect.

Colossians 1:1 and Colossians 1:4