"Did you know," the pastor said, "that there are commands in Scripture that cannot be obeyed outside of the regular and committed involvement with a local body of believers?" Now, the Bereans were considered noble for "examining the Scriptures daily to see if these things were so" (Acts 17:11), so I thought I'd hunt that down.
There were a few items that jumped out at me. I already covered the 1 Corinthians 12 concept of being part of the Body and needing to participate. You cannot use your gift as commanded if you aren't functioning in the local church. And everyone knows about the Hebrews 10 command not to forsake assembling together (Heb 10:25). Jesus gave instructions on church discipline (Matt 18:15-17) which fall completely outside the realm of possibility for someone outside of the church. We are clearly commanded to obey our spiritual leaders (Heb 13:17). And we have instructions on keeping elders accountable (1 Tim 5:19-21), impossible for those without elders.
The most dominant thing that came to mind, though, was the "one another" commands. The big one, of course, is "Love one another" (John 13:34-35; John 15:12; Rom 12:10; 1 Thess 3:12; 1 Thess 4:9; 1 Peter 1:22; 1 Peter 4:8; 1 John 3:11; 2 John 1:5). Big ... really big. Critical, in fact.
Beyond the "love one another" command, there are several more. Jesus said, "Be at peace with one another." (Mark 9:50) Paul told the church at Rome, "Outdo one another in showing honor" (Rom 12:10) and "Live in harmony with one another." (Rom 12:16; Rom 15:5) He told the Corinthian church to "comfort one another" and "agree with one another" (2 Cor 13:11). To the Galatians he wrote, "through love serve one another" (Gal 5:13) and "Bear one another's burdens." (Gal 6:2) He put two together for the church at Ephesus when he told them to be "bearing with one another in love" (Eph 4:2). He went on to tell them, "Be kind to one another, tenderhearted, forgiving one another, as God in Christ forgave you" (Eph 4:32) and to submit to one another (Eph 5:21). He warned the Colossians not to lie to one another (Col 3:9) and told them they should be "teaching and admonishing one another in all wisdom" (Col 3:16). He told the Thessalonians to "encourage one another and build one another up" (1 Thess 5:11) and "do good to one another" (1 Thess 5:15). The author of Hebrews said to "exhort one another every day" (Heb 3:13), to "consider how to stir up one another to love and good works" (Heb 10:24), and to be "encouraging one another" (Heb 10:25). James warned against speaking evil against one another (James 4:11) and grumbling against one another (James 5:9). Instead, he said to "confess your sins to one another and pray for one another." (James 5:16) Beyond loving one another, Peter added showing hospitality (1 Peter 4:9), serving one another (1 Peter 4:10), and being humble toward each other (1 Peter 5:5).
Now, to be fair, it is possible to obey some of those commands without being in a local body of believers. I mean, look, for some of us it seems like "Be at peace with one another" is best accomplished by avoiding one another. And it says "one another", right? So, just one ... right? But, seriously, that just can't be sustained for very long. Clearly the intent is not "one". And clearly the commands are in view of community, not individuals. "Live in harmony with one another" isn't very easy when you're talking about just two people. It suggests a crowd. "Bear one another's burdens" argues for connections (plural). Then there is "exhort one another every day" which requires an ongoing process, not an occasional one. No, I think you'd have to admit that this list of "one anothers", in its totality, precludes the Lone Ranger Christian concept (or, if you're married but not part of a church, the "Dynamic Duo" Christian concept).
Christian, if you are a disciple of Christ, a follower of the Word, intent on doing what God wants you to do, it would seem essential for you not to attend a church, but to be plugged into a local body of believers, actually connected and interacting and part of a local church. There are lots of "one another" commands to follow and you wouldn't want to miss out on all that grateful service to God because you have some better plan that doesn't include them, right?