Part of the ongoing series of sermons on the Beatitudes, Canon Michael Wiener of the Institute of Christ the King Sovereign Priest delivered this excellent presentation on the First Sunday of Lent:

Blessed are they that hunger and thirst after justice: for they shall have their fill.
Why are those who hunger and thirst for justice called blessed?
When we hear about this beatitude our thoughts might be directed toward a predominantly secular notion of justice: “Social justice”, “justice for the poor”, “global justice”, “environmental justice” or “restorative justice” – all aspects of justice, which may come to mind.  “Justice is the first virtue of social institutions, as truth is of systems of thought”, wrote John Rawls in 1971 (“A Theory of Justice”).
What kind of justice should we long for to be called blessed?
“Justice consists in rendering to God what is due to Him, and then for the love of God, giving also to the creature what is due to it.” (Fr. Garrigou-Lagrange, O.P.).
Justice in the broad sense of the word means the perfect fulfillment of the law. Law in this context means the law that governs the entire life of man. Just, according to this understanding, is he who is and lives according to the law that was promulgated either by God as the highest legislator implicitly in nature or explicitly (Moses) or by man in accordance with the law of God (law of states).
Justice, understood in this broad sense, is equal to holiness.
We say that Adam and Eve were just, because they reflected perfectly God’s idea of man in their physical and moral integrity. It was only after the fall of Adam and Eve through their disobedience to the will of God that man had to be governed by positive laws.
In the Old Testament justice meant the complete fulfillment especially of the law given by God through Moses. But perfect fulfillment of the law was impossible due to the fallen and weakened nature of man.
Perfect justice became visible in this world through the coming of Christ who fulfilled the law of God and the need for atonement completely. This perfect justice, re-established on the Cross by Christ, is communicated to us through Sanctifying Grace.
Through grace we are made just: “Love therefore is the fulfilling of the law”, says the Apostle (Rom. 13, 10).
Justice respects order! The author of all order is God and without respecting Him as source and center of all order, no man may be called just.
Pope Leo the Great teaches: “This hunger [for justice] is not for bodily food, this thirst is not for any earthly drink: it is a longing to be blessed with justice, and, by penetrating the secret of all mysteries, to be filled with the Lord himself. Happy is the soul that longs for the food of justice and thirsts for this kind of drink; it would not seek such things if it had not already savored their delight.”
“The appetite comes with eating” – The more intimately we are united to Our Lord, the more we are having in common with Him, the true God made man, the more we long for an ever growing holiness. Love for justice is born in the love for our own sanctification. No true justice can be exercised or possessed without longing for one’s personal holiness.
“Bear in mind”, continues Leo the Great, “the kind of school in which you are to learn your skills, the rewards to which you are called. Mercy itself wishes you to be merciful, justice itself wishes you to be just, so that the Creator may shine forth in his creature, and the image of God be reflected in the mirror of the human heart as it imitates his qualities.”
Justice is not self-righteousness, we don’t make ourselves just, but we receive justice by receiving God’s grace and cooperating with it. “If any man thirst, let him come to Me and drink. He that believeth in Me, as the Scripture says: Out of His belly shall flow rivers of living water.”
The just man’s thirst for justice won’t be completely satisfied here on earth, but in the beatific vision in heaven.  However, such a man will long for God’s grace not only for himself, but also in others. True justice which desires to give God what is His, wants also to exercise true justice towards his neighbor.
The just, if he is blessed, wishes to see the rivers of living water extend themselves also on the whole of creation. For this goal the just man works, prays and suffers. But such a man doesn’t separate any form of justice from God’s will and order. There is no such thing as social justice without respecting God’s will, there is no justice for man if man is opposed to God. 
He who wishes to establish perfect justice in this world without beginning to long for his own sanctification and without placing all hope and all desire in God as the source of all justice, is not blessed but self-righteous.
Blessed are therefore those who, as a result and fruit of their serious spiritual efforts and struggles, are moved – for example – to pray and work for the rights of the unborn, the sick, the dying.
Blessed are those who desire justice in this world which is based on an ever renewed understanding of the rights of God!
Blessed are also those who see the unjustly treated as individuals with a dignity as creatures of God, rather than seeing them as nothing more than pawns in political discussions about “social justice.”
The beatitudes are the most heroic and perfect gifts of the Holy Ghost in man. These beatitudes describe true happiness in this life and in the next. Those who long for justice will give themselves to works of justice. According to the teaching of St. Augustine and St. Thomas (ST II, II 139, 2) this longing for justice will be accompanied by the gift of fortitude – to help us overcome obstacles in the works of justice.
What do we need more in this life than God’s gift of fortitude to persevere in works of justice and to enjoy a foretaste of heaven in receiving this blessing of Our Lord?
Blessed are they that hunger and thirst after justice: for they shall have their fill.