In this Scripture we are told that anyone who comes to us that doesn't believe Jesus came in the flesh is both a deceiver and an antichrist. We are told not to receive them into our homes or even to bid them God speed. If we do, we are partakers of their evil deeds.
It is so important today that you know what you believe. That you are sure of your salvation. That you are so grounded in your faith and that nothing can shake you away from what you believe. Be very careful who you talk to and what their beliefs are. If they don't believe Jesus is the Son of God and the Saviour of this world, don't stay around them. Don't listen to anything they have to say. There is enough trouble in this world now, you certainly don't need to start doubting what you believe. If you lose your faith, what's left?