Time to look at some commentaries! As I mentioned before, I'll be preaching on the gospel text, Luke 18:9-14.
I love how Working Preacher begins: the commentator lifts up the basic meaning of the text, which is to be humble, and then adds an important warning. He writes, "The difficulty with such an interpretive tact, however, is that we might as well end up preaching, 'Lord, we thank you that we are not like other people: hypocrites, overly pious, self righteous, or even like that Pharisee. We come to church each week, listen attentively to Scripture, and we have learned that we should always be humble.'" If we're praising ourselves for our humility, we've clearly missed the point. (I'm reminded of C.S. Lewis' description of pride as a hydra - when you cut off one head, three more sprout up in its place.)
As Working Preacher points out and I noticed myself in the text, the Pharisee is being both honest and virtuous. The Pharisee is doing everything he describes (fasting twice a week, tithing) and those actions are exactly what he is supposed to be doing. The Pharisee is following the law, which are God's expectations of God's people. Would that all of us were fasting twice a week and tithing! Working Preacher puts it this way: " It isn't that the Pharisee is speaking falsely, but rather that the Pharisee misses the true nature of his blessing. As Luke states in his introductory sentence, he has trusted in himself. His prayer of gratitude may be spoken to the Lord, but it is really about himself."
The tax collector, in contrast, knows his own unrighteousness. We have to keep in mind that tax collectors were seen practically as traitors to the people of Israel, in cahoots with the oppressive Roman regime. He cannot rely on his own righteousness, so he must rely on the mercy of God. Again, Working Preacher puts it better than I could: "Here is the essential contrast. One makes a claim to righteousness based on his own accomplishments, while the other relies entirely upon the Lord's benevolence." What I see here is a tension between action and attitude. Both are important. We should strive to act rightly; but right actions with wrong (self-focused) attitude leaves us like the Pharisee. By contrast, the tax collector is acting wrongly but thinking/believing rightly. It may be appropriate not to see action and attitude of equal importance, especially from a Lutheran perspective - the attitude here seems to be more important than the actions.
However, there's a problem here, too. Working Preacher warns me, "As soon as we fall prey to the temptation to divide humanity into any kind of groups, we have aligned ourselves squarely with the Pharisee. Whether our division is between righteous and sinners, as with the Pharisee, or even between the self-righteous and the humble, as with Luke, we are doomed." Well then. Luke has put us in a difficult position, hasn't he? A parable with contrasting characters teaches us the danger of placing people into categories.
I also checked out two other commentaries: Joel Green's Lukan commentary in the NICNT series, and Joseph Fitzmyer's in the Anchor Bible series. One interesting point that Green raised is the Pharisee's actions go above and beyond: the Pharisee doesn't just fast one day a week, but twice; the Pharisee doesn't make distinctions about what income to tithe, but gives a tenth of everything. So his righteous actions are being highlighted almost to the point of caricature. Fitzmyer echoed some of the points above, and also had a note on that para I was wondering about (it is a comparative, hence the translation "rather").
There's one other important issue at stake here. For most of its history, the church has emphasized the danger of pride, considering it the worst of the seven deadly sins, or that hydra of C.S. Lewis. As a person who struggles with pride at times, I understand whence this emphasis comes. Pride can be insidious and can overwhelm everything we do. However, and this is a big caveat, not everyone finds pride to be their greatest sin. This point is often raised by feminist theologians because it often affects women more than men - but I think the point is an important one, even apart from the issue of gender. There are some people for whom excessive humility, rather than pride, is their consuming and destructive tendency. Women tend to be more affected than men by this issue because women, more than men, are socialized to be humble and serve others. For those who are not puffed up with pride but beaten down with too much humility, the problem of sin looks very different. If we drive home a message that says, "You must serve others, you must not think of yourself," the prideful people may be corrected - but others will be paralyzed and destroyed. Jesus tells us to "love our neighbor as ourself," and that formula requires both love of self and love of neighbor. So I, and I think anyone who preaches on this text, has to be careful that we speak to sin in all its forms, both self-centered and self-destroying.