These scripture references do tell us how to discern rightly “believers” which helps us to discern if or not they are a believer..... John 1,2, is addressed to believers....... But there are many who are professing Christ...who are not his...and new agers UFO speak often of “Christ Consciousness”... and use His name frequently to entice people of faith...because it works. It is not until they fry your brain they give you the rough stuff and by then your mind is jello so to speak.
Even Muslims believe Christ came as a teacher/prophet...which he is...they just don't believe He was God in Christ.....so basically what these verses are saying is You must believe that Christ is indeed God. And that is where many believers get off the train.
I guess I should have fleshed out my “ . . . “ to include the basic doctrines of the faith I usually do . . . including KING OF KINGS, LORD OF LORDS, BORN OF THE VIRGIN, CRUCIFIED FOR OUR SINS, ROSE THE THIRD DAY, UNDER WHOM ALL WAS PLACED ETC.
Thanks for your kind words.