Most commentators I've read about this section focus on the specific categories of people Jesus talks about. But think for a second about the relationship this passage has with what Jesus says in Revelation:
“‘So, because you are lukewarm, and neither hot nor cold, I will spit you out of my mouth.
“‘For you say, I am rich, I have prospered, and I need nothing, not realizing that you are wretched, pitiable, poor, blind, and naked.
“‘I counsel you to buy from me gold refined by fire, so that you may be rich, and white garments so that you may clothe yourself and the shame of your nakedness may not be seen, and salve to anoint your eyes, so that you may see.
I don't think what Jesus was driving at here at the beginning of the Sermon on the Mount was so much how blessed the poor, the mourning, the meek, the hungry, the thirsty, the merciful, pure in heart, the peacemakers, the persecuted, and the reviled are. With Jesus (and we'll see this again and again), most of the journey is in recognition. If you don't realize you are hungry or thirsty, if you aren't aware you're in mourning or poor, if it hasn't occurred to you to offer mercy to another in their sin, if you don't know there is something wrong with your heart, don't know the trouble you've caused in relationships, have never thought to speak the name of Jesus boldly so as to risk persecution, you'll never know his blessings either. We either recognize our need for Jesus or we don't.
The reason Jesus was so hard on the religious leaders of his day was because they believed themselves to be righteous in themselves. Though they talked about God all the time, they had never really faced their personal need. Well, most of them, anyway. Remember that it was Nicodemus (a member of the ruling counsel) who came to Jesus at night because he realized his need. So many people never ask the question or admit they have a need or a problem because they're afraid someone might judge them or think less of them. Well, on behalf of your brothers and sisters I want to make an offer: we're here and we're just as damaged and hurting as you are. That's why we've fled to Jesus. Come... let's talk.