There's a difference between membership and participation.
You can be a member of a gym and never go.
You can be a member of a scholarly society and never attend its meetings.
You can have a membership at Sam's Club and never take advantage of it.
None of these ways is how the Bible speaks of church membership. The members of Christ's body are expected to be far more actively involved than that.
Membership without involvement would have been unthinkable in the early church.
Membership in the New Testament is like a business partnership. Believers are like stockholders actively engaged in a common commercial enterprise.
That's why I prefer to render the word koinōnia in Phil. 1:5 as "partnership" rather than "fellowship" as in the KJV, ASV, NKJV, and LSB.
In Christian circles, we've often reduced the idea of fellowship to a time after the service. My home church in Hawaii had both a "sanctuary" and a "fellowship hall."
If asked, "Are you enjoying your church?", the reply might be, "Well, the fellowship is great, but the services are lackluster at best."
The partnership that Paul praises in the book of Philippians is the result of having a vested interest together in a common enterprise -- the gospel. My goal in teaching the Greek exegesis of Philippians this semester aims at exploring the values of a gospel partnership, because "gospel partners" is just another way of saying "Christians."
More to come ...