Not all unbelievers are non Christians.
In fact there is someone inside the Christian Church who can be considered as unbeliever.
Matthew Chapter 18
[SUP]15 [/SUP]“If your brother or sister[SUP][
b][/SUP] sins,[SUP][
c][/SUP] go and point out their fault, just between the two of you. If they listen to you, you have won them over. [SUP]
16 [/SUP]But if they will not listen, take one or two others along, so that ‘every matter may be established by the testimony of two or three witnesses.’[SUP][
d][/SUP]
[SUP]17 [/SUP]If they still refuse to listen, tell it to the church; and if they refuse to listen even to the church, treat them as you would a pagan or a tax collector.