There are many deceivers in the world and our Father tells us some of the ways to recognize them. We are to test them by their fruit, which is perhaps the most obvious way for rotten apples stink to high heaven.
But, for the more dangerous subtil ones He tells us....
Is it saying that Jesus was never born? No one professes that....not even Muslims. Everyone knows that there was a literal Jesus born in the flesh. I see two reasons, perhaps the correct answer is found in both of them.1. As believers He is part of our flesh...He abides in us. Is that what is meant by there being deceivers that "confess not that He come in the flesh?" Is it that He comes in our flesh and deceivers deny that? 2. Is it that deceivers don't confess the REASON He came in the flesh. That reason is......

2 John 7. 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.9. Whosoever transgresseth and abideth not in the doctrine of Christ, hath not God. He that abideth in the doctrine of Christ, he hath both the Father and the Son.10. If there come any unto you, and bring not this doctrine, receive him not into your house, neither bid him God speed:11. For he that biddeth him God speed is partaker of his evil deeds.
Those that abide not in the "doctrine of Christ" are those taught of in [1 Timothy 4:1] that are seducing spirits bringing the doctrines of devils. So we see that what the deceivers do is say that He "didn't come in the flesh." What does that mean?

1 John 3:5 And ye know that He was manifested to take away our sins; and in Him is no sin.
He was "manifested" or....came in the flesh...to take away sins (our is not in the texts) so He came to take away the sins of all that follow Him...not just the sins of the elect. A deceiver won't confess that FACT. And to my surpise there are some that see the elect as being the only ones destined for heaven. 1 John 4:3 And every spirit that confesseth not that Jesus Christ is come in the flesh is not of God: and this is that spirit of antichrist, whereof ye have heard that it should come; and even now already is it in the world.
Satan and his crew aren't stupid. They are coming after His elect. It wouldn't be very subtil of them to pursue an elect by telling them that Christ never came in the flesh...if that was what is meant. No, it is the purpose of His coming that they twist. The reason He was manifest into a flesh body is what they argue against.I pray none of us are overcome by this deception but it is among us. Pray for our fellow saints that we will know our enemy and his subtil ways, that we will know he comes pretending to be of Christ...a Christian. He has foretold us all things and warned.... "take heed lest any man deceive you." Genesis 3:15 Now the serpent was more subtil than any beast of the field which the LORD God had made.......