You're missing it completely. Believers have an anointing that enables them to know if what John, or any other person says to them is the truth.
That's not what scripture says.
That's your invention.
You are completely missing this element of 'knowing' through the anointing of the Holy Spirit and putting the 'knowing' on what someone tells you, which, of course, for you means what the Catholic church tells you. And that is indeed what Catholics do. They rely on being told what is the truth and what is not, instead of relying on the anointing within the believer to tell them what teachings are truth and which are not. That is a formula for disaster as the history of the church has proven.
The Catholic Church has the teaching authority from Jesus Christ.