To hunger and thirst for justice

from Divine Intimacy, an exellent reminder of what this means in the beatitudes:

Blessed are they who hunger and thirst after justice Mt 5:6.

Hunger and thirst indicate imperious needs which cannot be suppressed, it is a question of life and death. As food and drink are absolutely essential to the life of the body, so justice is absolutely necessary for a life of virtue, and its duties are so compelling that no motive can exempt us from fulfilling them. If an act of charity for the neighbor should impose on us great inconvenience or cause us serious har, we would not be obliged to do it, but the same inconvenience or harm chould not excuse us from fulfilling a duty of justice.

It is thus appropriate to speak of hunger and thirst for justice, not in the sense of vindicating rights, but in the sense of cultivating in ourselves such a lively desire and imperious need for justice in all our relations with others, that we do not feel satisfied until we have completely fulfilled all the duties stemming from this virtue.

In other words, if you haven't noticed, the hungering for justice spoken of in the beatitude which makes one blessed is not the desire to see others act in justice, but the overwhelming desire to act with justice yourself.