Mat 5:6 Blessed [are] they which do hunger and thirst after righteousness: for they shall be filled.
Alternative: Those who are happy hunger and thirst for justice for their soul will be fattened.
The fourth beatitude talks about "righteousness," which is a difficult concept in modern society. Today everyone is quick to criticize those who are "self-righteous" because they are defined as being quick to judge others. This is not what Christ meant.
In Greek, the term used for righteousness is dikaiosune, which means "being in an ideal state." We can think of this as the state that God wants us to be in or what we were designed for by nature. Of course, in historical terms this means being virtuous, honest, pure, and thinking and acting correctly. Our modern idea of justice, that is, giving every person their due, is a somewhat lower standard of righteousness, especially when it is applied to trying to achieve some condition of social justice where everyone's due is considered the same regardless of what their behavior merits.
This idea of righteousness is both more individualistic and more morally absolute. We all have different talents and abilities that we are expected to use and develop. However, there is a standard of character, a standard of behavior, that we are also expected to aspire to irrespective of our particular abilities. We may never be able to reach that standard, but we need to try.
In this phrase, Christ is saying that people naturally yearn for this state of righteousness. We desire to be right with ourselves and right with the world. We have a hole in our lives that we are seeking to fill and satisfy, shortcomings that we are seeking to overcome. Chortazo, the Greek word translated in this version as "filled" is also means "to satisfy" with a close association with the physical satisfaction of eating. This takes us back to Christ's metaphor for eating, especially bread, and receiving God into our lives. Here he promises that the state of righteousness is possible for all of us.
"Blessed" is from makarios (makarios) which means "blessed," "happy," and "fortunate."
"Hunger" is peinaô (peino), which means "to be hungry" or "to be starved," and it is a metaphor for desire and cravings.
"Thirst" is from dipsaô (dipsao), which means "to thirst," "to be thirsty," and "to thirst after" a thing.
"For" is from hoti (hoti), which means "for what," and "wherefore."
"Righteousness" is from dikaiosunê (dikaiosyne), which means "righteousness," "justice," and "the business of a judge."
"They" is from autos (autos), which means "the same," and the reflexive pronouns, "myself," "yourself," "himself," "herself," "itself," or the oblique case of the pronouns, "him," "her," and "it." It also means "one's true self," that is, "the soul" as opposed to the body and "of ones own accord."
"Filled" is from chortazô (chortazo), which means "feed," "feast," "fatten" and "to eat their fill." It is a term most commonly used for cattle.