Please read 1John 4:1-3
I would like someone to clarify something for me. This verse says that any spirit that confesses the Christ has come in the flesh, that spirit is from God.
As I understand it, this verse if taken by itself, can justify a persons acceptance of Islam.
Muslims confess that the Christ has come in the flesh.
However, so do Bahais and Mormons. So a Muslim can't use this verse to justify Islam without also justifying other religions which a Muslim would not accept.