This is the fourth beatitude that Jesus taught in the Sermon on the Mount. Here Jesus uses words rooted in the physical world to describe a spiritual need in all of our souls. Just as our bodies need food and water for sustenance and growth, so our souls need righteousness, and without it, we will perish. “Unless your righteousness exceeds the righteousness of the scribes and Pharisees, you will by no means enter the kingdom of heaven,” Jesus said elsewhere.
Notice that Jesus does not say, “Blessed are the righteous,” as if righteousness was something already attained, but he says “Blessed are those who hunger and thirst for righteousness,” indicating those who realize they are constantly and desperately in need of it. The blessed are not those who have arrived, but those who continue, whatever the cost, to yearn for righteousness.
But Jesus declares that those who long for the righteousness of God, and seek for it despite their flaws, shall indeed be satisfied. The deep longings of their soul will be gratified by the One who put those yearnings there. This beatitude makes it plain that those who desire righteousness as their all-consuming hunger and thirst shall be deeply and completely filled—satisfied—by God Himself.