Why was 1 John 4:1-3 written? Which people does he refer to who did not
believe Jesus came in the flesh? If this was written in the first
century, why would anyone not believe that he came in the flesh with so
many eye-witnesses still alive? Is it because they could not understand
or believe God became man?

2nd question:

I am studying the Bible with someone and was wondering if it is necessary
for him to know before getting baptized who Jesus was in the sense of him
being the Son of God–God in the flesh?

It is always hard to say for sure why someone did something,
especially when it was done two thousand years ago. To some extent, one
must speculate about why John wrote what he wrote in this book. From 1st
John 4:1-3 we know that there were people at the time the letter was
written who were claiming that Jesus was a spirit, but that he did not
occupy a physical body. Scholars will tell you that the heretical group
John is referring to is the Gnostics. These were a group who wanted to
combine their Greek/pagan/mystery religion with Christian thinking. We
know quite a bit about the Gnostics from their writings. They taught that
Jesus did not dwell in a physical body. They therefore denied the
physical death of Jesus on the cross. You can see right away why John
called this group the Antichrist!

Your second question is why people could believe such a heresy
so soon after the time that Jesus lived on the earth. That is a good
question. I believe that you can assume that the eyewitnesses to the
ministry of Jesus were not among the members of the Gnostic sect. The
evidence is that these people were not from a Jewish background at all,
but that they were superimposing their own Greek philosophy/religion on
the Christian teachings. These Gnostics were very strongly opposed by the
Christian church from the very beginning as you can see from the book of
First John. In the end, as said before, it is hard to say why a
particular group from a long time ago did what it did, but it may help for
you to realize that these people were definitely not among the eye
witnesses to Jesus and that they probably had a very strong predisposition
toward a particular philosophy which was able, for them, to overwhelm the
clear testimony of the apostles and other eye-witnesses, few if any of
whom they had met personally.

On the second question, it seems clear from New Testament
writings such as 1 John that understanding who Jesus was is absolutely
central to Christianity. It is my experience that before I or anyone I
know baptizes anyone we ask them to make some sort of confession such as,
“Do you believe that Jesus is the Son of God, that he lived on the earth,
that he suffered and died for your sins.” We do not have a particular
formula, but tend to ask a question along these lines. I am not in a
position to state unequivocably whether a person who is baptized but did
not understand who Jesus was is not saved, but I would be, at the very
least, concerned about that situation. In your situation, with the person
you are studying with, this is not a problem. You simply need to teach
him/her correctly. If you have a situation in which you are concerned
about someone’s baptism based on their prior understanding of who Jesus
is, I suggest you find a local church leader whom you trust to share your
concern. It is not my position to discuss individual cases of people I
have never met. Does this answer your question? Feel free to e-mail me
directly.

John Oakes