St. Paul teaches us to do good to all people, not only believers.
Galatians 6:10 "Therefore, as we have opportunity, let us do good to all people, especially to those who belong to the family of believers."
Likewise, St. Peter teaches to show respect to all people.
1 Peter 2:17 "Show proper respect to everyone, love the family of believers, fear God, honor the emperor."
This of course ties in with universal salvific will of God (1 Timothy 4:10, 1 John 2:2, Hebrews 2:9) - we should show love to everyone, sicne God is willing to save every single person in our way.