Hereby know ye the Spirit of God: Every spirit that confesseth that Jesus Christ is come in the flesh is of God: And every spirit that confesseth not that Jesus Christ is come in the flesh is not of God – 1 John 4:2–3
I think you are taking the verse out of context and extending the meaning. Simply, those that cannot confess about Jesus is not of God.
One can say they believe in Jesus and in their heart, do not believe it. Look at Matt 7: 21…where it states not all who says Lord Lord will enter heaven.
Satan can fool you and I, mask himself as an angel, and say he believes in Jesus to fool you and I.
As I stated in a previous post, there are those in the CC who have seen angels, the Virgin, Jesus and the Trinity (Sister Lucia)…but look at the lives they led after their visions and contrast it what what JS did after his vision.
The most important contrast is they did not go out to establish their own religions and remained obedient and humble to the authority of the CC and its Magisterium. Some of them have bodies that have remained incorrupted, some received Christ’s wounds on their bodies. What greater honor do you think is there than to receive Christ’s wounds on their bodies?