I would also add in general agreement to many of the comments above that TWI's definition of an "unbeliever" was a mix of theology and what I'd call social prejudice.
I'll explain -
Those of us involved from the late 60's through the 80's know that the Way advertised itself as a non-sectarian and non-denominational group.
At the same time the Way was creating it's own denomination, so defined because -
if it succeeded in it's goals of "Word Over the World" (not Craig's later lack of interest in continuing to try and just declaring by sacred fiat that voila! it had been achieved)
then it would in essence create a new, "true" body of the Church that would stand out separately from all other denominations and churches by it's own, "accurate" and correct theology.
While the Way liked to give lip service to the truth and fact that the New Testament teaches that the "church of believers" is ALL those born again of Christ, using the simplest and sparest of essential points of doctrinal requirement.....
They/We didn't live that, didn't apply that, didn't believe that part of God's Word.
VPW taught that the "family" of God might include all born again believers, all "sons", all those who were born again but -
The "household" was all the accurately taught and actively believing believers. "Standing" believers. And he taught from the epistles from the perspective that the "true believers" in the Way were the same "household" as the "true standing believers" in Pauls day.
Within that he created sub groups of "corps", and "staff" and "WOW Ambassadors", and other forms of commitments that allowed for specific application of time, talent and service within that household of "standing believers" .....
Who in our day and time just happened to be Way PFAL grads and who fulfilled some basic requirements of what I would call "non-membership", laughingly....those are people who go to a Way fellowship at least once a week (it had been once a month at one point), manifest "power from on high" and speak in tongues, and who financially support the ministry.
Anyone who was around from the late '60's will remember how that language got introduced and how it slowly evolved into a set of expectations, requirements, traditions and rituals - all the components of a developing religious denomination.
It just did. I get frowns from Wayfers who have left at some point and who feel it didn't go that route, and especially those who adhere to all or some of what they learned from the Way.
I do too but even allowing for differences of opinion I see it as both naive and facetious to not see that was happening as it did. And it's self serving to not recognize it now.