Christians do believe that verse and understand it in the proper context.
For example....We don't know what time Jesus ate lunch...did he brush His teeth? What clothes did he wear on Tuesday?
What kind of late night talks did He and the disciples have? If any.
How far did He walk on a given day?
What all did the disciples say in the upper room? Do we have EVERY recorded word?
The list can go on and on and on. That's why John wrote what he did. Anyone thinking will understand the Bible does not give, nor was intended to give, a 100% complete record of every waking moment in the life of Christ or the disciples.
However, John did tell these things are written so you man know what you believe.
Everything needed for salvation can be found in the Bible. If catholics would stick to the Word, they might understand that.
That would destroy Catholicism.
There was not a pope in the early church. That is a man-made non-biblical position.
In reality, the modern catholic priesthood is very similar to the priesthood of the jews we encounter in the Bible.
Protestant soloists claim that anyone, alone with a Bible and the Holy Spirit, can authentically interpret Scripture. Well then, why does the Holy Spirit tell some people that baptism is necessary for salvation and others that it is not necessary? Why does the Holy Spirit tell some that the Eucharist really is Christs body and blood and others that it is only a symbol?
There is a certain arrogance in this statement. It gives the implication that only certain people are "smart" enough to understand the Scriptures. A review of the Bible shows that is not the case.
For example, Mary and Joseph both understood the Scriptures. The Bereans constantly searched the Scriptures. Paul admonished people to read the Scriptures. So yes, anyone who is willing to sit down and read the Bible can understand it. A working knowledge of the Greek and Hebrew really helps bring the Word into focus, but is not required.
I see why the catholic church for years resisted the common man from reading the Word!
One presumes the Holy Spirit has said these things. In reality the Holy Spirit will not contradict the Word.
The problem we run into is that man thinks he knows how to interpret the Word. The main problem I see is people taking verses out of context or reading something into a verse to prove or substantiate their point that is not supported by the text.
Case in point is catholic teaching on the assumption and immaculate conception of Mary. Neither are supported by Scripture. Same could be said of infant baptism.
Why does the Holy Spirit say to some Protestants Once saved, always saved and to others, No?
See answer above.