I thought I'd take a look at this verse, and ponder a few things that come from what it says.
I. This verse gives us a good look into how we don't take the Word at face value these days. How many of us greet our fellow church members with a kiss? (International readers, we know some of you do.) Why do we not do what the Word says?
II. Ah, we don't do it because we're not convinced that, while it seems to be a plain command, we shouldn't just automatically do it. Why not? Typically, we don't do the plain commands of Scripture because we think we shouldn't have to do them. Now, some of you are wondering how to get around this, aren't you?
III. This verse shows the need to extract the meaning through the cultural context. The greeting with a holy kiss would be culturally the action of greeting between people that know, trust, and honor each other. So what is Paul's command worth to us? Is it just that we should greet one another in the appropriate manner to shows fellowship, trust, honor, and love? Many churches in America say this is why we greet with a handshake or a hug, if you're a hugging church.
IV. I don't think this is right. I think Paul is reminding the church at Rome that is appropriate in church to greet one another in accordance with our relationships. In other words, he's not commanding that the Romans greet each other with a holy kiss to check off the holy kiss on their activity in church card. He's pointing out that, since they do have true fellowship with one another, let it be shown.
V. The point is this: we have developed a habit of reading Scripture searching for actions to take. Now, that's a good thing, as far as it goes, but the same God who said "Rend your hearts and not your garments" (Joel 2:13) is the one we follow. The actions we are seeking should be reflective of where our hearts stand, not our surface level of actions. Rather than figuring out whether we should kiss or handshake, we should be focused on building the attitude that results in the right actions.
VI. A final warning: we cannot go disregarding the actions mandated by Scripture. While we do need to discern whether the actions are cultural or timeless, and how they apply to us, we cannot just toss them out. Whether we are looking for a loophole because we don't like them, or because we're not really up to it. Our hearts ought to lead to action, else our hearts aren't really where we claim they are. This is, however, not perfectly evident here. It's the whole message of the book of James, though. The "intentions" are useless if they do not lead to action.