If you will please excuse the long subject title of this post …
“No man can be charged with heresy, even on a fundamental, till after faithful admonishment he persists in it, knowing that he does so” (John M. Brentnall, Just A Talker: Sayings of John (‘Rabbi’) Duncan, p. 185).
Not so, Mister Duncan. A doctrinal transgression “on a fundamental” DOES NOT require a knowing and stubborn refusal on the part of the transgressor before being charged as not having God:
“Everyone transgressing and not abiding in the doctrine of Christ does not have God. The one abiding in the doctrine of Christ, this one has the Father and the Son” (2 John 9).
Consider what some theologians call “the analogy of faith.” Consider further how the following Scriptures harmonize with 2 John 9 (also John 10:4-5 and Romans 10:1-4) on the serious topics of judging, rebuking, restoring to fellowship, and excommunication:
“A man that is an heretick after the first and second admonition reject; Knowing that he that is such is subverted, and sinneth, being condemned of himself” (Titus 3:10-11).
“Moreover if thy brother shall trespass against thee, go and tell him his fault between thee and him alone: if he shall hear thee, thou hast gained thy brother. But if he will not hear thee, then take with thee one or two more, that in the mouth of two or three witnesses every word may be established. And if he shall neglect to hear them, tell it unto the church: but if he neglect to hear the church, let him be unto thee as an heathen man and a publican” (Matthew 18:15-17).