A complete outline of a salvific message, relevant Catholic doctrine, and a practical application, based on the Lectionary readings for the Fourth Sunday in Ordinary Time, Year A, can be found here. It is titled A Vocation to Beatitude.
The central idea is the Beatitudes. The Catholic doctrine drawn from that idea is that Christ’s Beatitudes can teach and transform us. The practical application is purification of heart.
I think one of the best insights into the Beatitudes that will help us begin to comprehend each one and to grasp how they are related to each other (and to our lives) is that the Beatitudes are first of all a portrait of the Person of Jesus Christ Himself. In the Beatitudes in the Sermon on the Mount, Jesus tells what kind of person he is, someone as approachable as the newborn babe in Bethlehem.
Our Lord said about himself in another place that he is meek and humble of heart. That must also be our grace-assisted goal in life, to leave this world as rid as possible of pride, greed, wrath, envy, lust, gluttony and sloth, with the virtues of chastity, temperance, charity, diligence, patience, kindness, and humility in their place.