Today at a Saturday morning study with some guys, one of them mentioned the Engels Scale, of which I had never heard. So I looked it up. Basically, it's just a number line applied to a person's receptiveness to the Gospel.
+5 Stewardship +4 Communion with God +3 Conceptual and behavioral growth +2 Incorporation into Body +1 Post-decision evaluation New birth -1 Repentance and faith in Christ -2 Decision to act -3 Personal problem recognition -4 Positive attitude towards Gospel -5 Grasp implications of Gospel -6 Awareness of fundamentals of Gospel -7 Initial awareness of Gospel -8 Awareness of supreme being, no knowledge of Gospel
I'm not entirely sure how useful it is, except to inform one's personal ministry, but as a Christian I believe that part of my purpose is to influence others to accept Christ and become disciples (Matthew 28:19-20). If I can understand where a person stands in relation to the Gospel, it makes it easier to know my role in my relationship with them.
There's an “improvement” on the Engels scale, called the Gray Matrix, which divides openness to the Gospel from internalization of its message and places them on two different axes (a Cartesian plane), but the idea is pretty much the same.
Just thought I'd pass on some interesting ideas.