Some people have the notion that the Ten Commandments are pretty much all you need for Catholic moral teaching. Hew to them and you’ll be a moral person—and being a moral person is what it’s all about, right?
Actually, wrong. Morality is a good thing, but the Catholic faith does not call us to be merely moral. It demands something much greater:
For I tell you, unless your righteousness exceeds that of the scribes and Pharisees, you will never enter the kingdom of heaven. (Matthew 5:20)
Of course, we are given that righteousness by grace through faith in Jesus Christ, since nobody can be justified before God merely by clenching his teeth and trying to obey the law. But the fact that we are justified by grace through faith does not mean “Now you can blow off the commandments”. It means, “Now you can transcend the commandments.”
In other words, in Christ, the commandments form the bottom, not the top of the Christian moral life. You can’t go below them, but you can reach far above them. The idea behind the commandments is, “If you can’t love God, at least don’t blaspheme him by worshipping false gods. 
If you can’t love your neighbor, at least don’t rob him, canoodle his wife, or beat him to death with a baseball bat.” We’re not exactly looking at the snow-capped summits of human moral endeavor there. We are instead looking at lowest expectations that can be placed on the human person for minimum decency—and even those are more than many people can muster.
“Many people” includes many of us Christians. We are inveterate jailhouse lawyers when it comes to God’s demands for sanctity. We constantly hold out for Minimum Daily Adult Requirement Christianity, something like a bride who asks on her wedding night, “How many times do I have to kiss my husband in order to fulfill the Church’s definition of a “good wife”? There’s a fundamental tone deafness at work whenever we greet the love of God with plea bargaining and attempts to minimize his demands for obedience. God’s grace is not given to us with a pat on the head and the exhortation, “See that you get as close to mortal sin as you can without technically committing it.” Rather it is given in order to make us saints.
And so, the Beatitudes are given to teach us that the goal is to actually love God and neighbor, not merely get away with venial sin and minimal obedience. They remind us that the purpose of the Christian life is not mere ice-cold, rule-keeping morality, but happiness—total, unending, ecstatic, fiery joy that is far closer to the ecstasy of having the greatest sex you could ever have with the greater love you could ever hope for than it is to getting one’s sums right in a math quiz.
(If you think I’m being irreverent in comparing Heaven to the marital act, reflect on the fact that marriage is a sacrament and that both Old and New Testaments constantly compare our relationship with God to that of man and wife. Of course, as ever, God is vastly more unlike than like any of his creatures, including the creation called “marriage”. But nonetheless, marriage is not chosen at random by God to reflect and communicate some of his glory.)
In short, the Beatitudes point us, not to the bottom of the moral ladder, but to the top, which reaches into Heaven itself.
Of course, when the world thinks of Heaven it thinks of beautiful scenery, or various perks, or of a vague luminosity. And, to be sure, Heaven will be the most beautiful place imaginable (and it will indeed involve a New Earth, not simply vaporous spooks floating in the Vast Nowhere). But that’s not what captures the biblical imagination. Rather, the supreme joy of Heaven is that we shall see God Himself “face to face.” That is the essence of beatitude. So Jesus is, in the Beatitudes, training our eyes so to speak, to see the face of God in the poor, the mourning, the meek, the persecuted, and all the others whom He names “blessed.” .
Of course, that strikes a lot of people as a downer. We’d much rather see God’s face in some cool mystical trance without all the fuss and bother of those tacky people. But the Beatitudes are firm on the matter: If you want to see God’s face, that is where you must look.
Therefore, for the next eight weeks or so, we will be looking at the Beatitudes with an eye to training our eyes to look for the kingdom of Heaven.