A small thanks to the resident Theists..

[John V]

Perhaps reading the sentence as a sentence, instead of looking at individual words might help? Or would that be going too fast for you? Here, let me help:

"For many deceivers are entered into the world, who confess not that Jesus Christ is come in the flesh. This is a deceiver and an antichrist." -- 2 John 7

Now, who doesn't believe that Jesus has come in the flesh? I can see you thinking about it, raise your hand when you have the answer... Yes, that's right!

Gnostics don't believe that. Most commentators think the reference was against gnostic Christians, hence "in the flesh," as they thought Jesus was a purely spiritual being.