From First Epistle of John
( v 1-4)
“…We proclaim to you what we have Heard,
Seen, and our hands haveTouched…
The Word of Life…this Life became visible; which we have seen and bear witness to it.
And we proclaim to you the eternal life that was present to the Father and became visible to us.

What we have seen and heard in turn we proclaim to you so that you may share life with us.

This fellowship of ours is with the Father and with his Son, Jesus Christ.

Indeed, our purpose in writing you this is that our joy may be complete.”

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If you lived 2000 years ago and lived in a small Christian community in year ca 90-100 where some of your leaders believed in God but refused accepting faith in Christ, how would you react?
Would you wonder? Ask for more proof?