God is dishonored, and his Spirit is grieved, when this atmosphere is tainted by careless living and by evil-speaking. The intent of that statement was to remind its hearers of the sacredness of their church membership. We're not saved through being a member of the formally organized church, but it is still God's desire that we link our life and influence to the structure that He has erected on the earth. The church needs its salt. It's different than joining the Rotary Club.
People can and do just up and leave from some types of organizations.
And so the most loyal members will be those insisting that the pillar and ground of the truth be the pillar and ground of the truth. This is a war, guys. Being a member of the Seventh-day Adventist Church gives me an opportunity to serve Him within His stronghold. Other venues exist where we can serve our Lord, including self-supporting ministries. But the Lord's first intention is that we remain within the structure He has established and make sure it continues to exist as the structure He has established.