Okay, so I've waited probably longer than I should have to answer this question. Thank you to everyone who responded, and mega bonus points to ChiAlphaCurt for giving me a wider distribution by x-posting it on his Xanga.
So the question: What is the most important thing you can do in a church service?
And my answer: To demonstrate God's love to others by loving them.
The Jews came to the Pharisees asking Jesus for the A-number one tops most important commandment (Mark 12:28-34, Matt 22:34-40). I think some wanted to trap Him, while others wanted an excuse for why they only had to follow one command and not 600 of the others. Amazing that this is the last of a barrage of questions they ask Him over the 3.5 yrs of ministry, and it's the absolute question to determine His motives in all things. So what happens? He flabbergasts them beyond the point where anyone can muster the courage to ask another theological question.
Here's the thing that got me: the lawyer/scribe asked Jesus for one commandment, and he got two. If you ask most Christians what THE most important commandment, they will readily tell you Mt 22:37, forgetting v. 39 completely. Why? Because that's how we operate: what's the one thing I should focus on?
When I posed this question, many answered something to the effect of "love God." Well that's great, but does it simply stop there? By no means! Jesus didn't stop there with the Commandments, He affixed the two together. They are ultimately inseparable, for to love God means to obey His Commandments (John 14:15), and to love what He loves -- people! These two Commandments are equivalent in stature, and they cover the bases for everything else. Think of it this way: when Jesus questioned Peter's devotion, He put an if-then on Peter's actions: "Do you love me? If so, then feed my lambs."
The whole reason this came up was b/c I went to a church where initially I felt unreceived. I knew the college pastor, so I said hey to him before the service started, but I still ended up sitting alone. When it came to "stop the service so you can greet the people around you" time, I got passed over. Granted, half an hour after church, I was in the car with some people I had just met headed to New Orleans (yeah, mom & dad, I ride in cars with strangers now). Nevertheless, I didn't feel that before the service, and although I really wanted to get into worship, I just couldn't get there. It was like I was tied down, watching how great of a time everyone else must have had. If you'll forgive me for saying so, I felt spiritually handicapped, like the beggar sitting at the temple hoping some kind person will stop by and heal them.
I spent the whole time praying, "God, I don't want to be self-centered here, but I really just feel like I can't get there without somebody else's help. I don't understand why I can walk into some churches and fall right into the Spirit in worship, but elsewhere I feel totally separated." He revealed to me that in some churches I visit, I feel practically ignored, while in others I'm smothered in affection from those who come there to worship God together; in both cases, it makes no difference how long I've been going there. One great example was Freedom Church out in Livingston. Two men greeted me out in the parking lot as they showed me where to park, four people or so served coffee & donuts out front, and then two more opened doors into the church and handed out bulletins. When I sat down in the back row, a guy I didn't know (yet) initiated a conversation with me, and not just a "hi nice to meet you," but actually being interested in what I had to say.
Here's the bottom line: it is every Christian's responsibility to help other people come into the service prepared to worship, and it's so simple. It's difficult, alright, but it's still simple. We have to love each other with the love Christ has shown to us so that by receiving that demonstration of God's love, we can respond to Him in kind. As far as church members are concerned (whether or not you have your name on the roster, if you act like a member, this includes you), we MUST be proactive. Yeah, I hate the "stand up and greet somebody around you," because we'll only greet those we feel comfortable greeting, and the rest get the cold fish handshake. That is the fastest way to get somebody to walk out the back doors and never come back again.
It doesn't matter how awesome of a time you have in worship, if somebody else misses out because you failed to bring them in, you're no better off than a Pharisee.