Biblical Foundation for Membership?

Rather than addressing the question of "membership" directly with a scriptural reference, I would like to suggest that there is a problem with the "Safe Church Policy" if a principal requirement is "membership in the church." What constitutes membership?

1. baptized;

2. completed profession of faith, but under 18;

3. active professing member, over 18;

4. inactive professing member; or

5. lapsed member.

Is a baptized child a member in the sense of being an "active professing member," i.e. one who has made profession of faith; has full voting rights at congregational meetings; can stand for office, etc. Do members in #2. & 3.- #5. meet the former criteria, even if they are membership categories. One might still want #2. - #3. to participate in the life of the church where the Safe Church Policy applies.

Secondly, can you think of a situation where someone might be worshipping with you for a short or longer period from another denomination who holds their membership where enfolding them into the membership of the Body of Christ on an interim basis only makes sense.

A Safe Church Policy should non-discriminatory in applying to members and non-members alike. 

I hope this take on the issue is of some assistance.

PS Maybe there's a deeper story behind the stance on membership. Personally, I know of someone who did not transfer their membership from their previous church due hurts arising in the former church and saw membership as problematic but wanted to be part of a worshipping community.