Hunger and Thirst for Righteousness
Matthew 5:6 (ESV) … “Blessed are those who hunger and thirst for righteousness, for they shall be satisfied.”
The fourth beatitude tells us that we are to aim at being righteous. We are to “hunger and thirst after righteousness.” A person who is desperately hungry or thirsty can think of nothing else. Hunger and thirst are the most basic and demanding drives of our physical nature. No one can ignore them for long. Happy is the man who has an equally strong desire to be like God.
None of the world’s religions can satisfy the human craving to be good. It is not in man’s fallen nature to be righteous, and all religion can do is cultivate his fallen nature. We are made righteous practically by the Holy Spirit.
According to the Epistle to the Romans, righteousness is first revealed, then required, then received, and only after that, reproduced. (The word righteousness occurs in thirty-three verses in Romans.) We are constituted righteous positionally by receiving as ours the righteousness of Christ. Our standing before God is thereby made perfect. We are made righteous practically—and righteousness is the key to practical Christianity—by the work of the indwelling Holy Spirit, who imparts to us the divine nature and enables us to overcome our old Adamic nature. This work deals with our state, which is all too often imperfect. Our standing and state will be in perfect harmony when we receive our resurrection bodies. Then we will be like Him for all eternity.
In the meantime the regenerated individual hungers and thirsts after righteousness in the happy anticipation that this desire is not going to be left unfulfilled. One of the horrors of Hell is the fact that God will ultimately say to the lost, “He that is unjust [unrighteous], let him be unjust [unrighteous] still” (Revelation 22:11). Lost people will crave righteousness with utter hopelessness. Not one drop of the water of life will be able to reach them where they are. 
 Phillips, J. (2014). Exploring the Gospel of Matthew: An Expository Commentary (Mt 5:6). Kregel Publications; WORDsearch.