How much do we want righteousness? How intense is the desire for goodness? Those who hunger and thirst for righteousness (vs. 6) have a spiritual appetite, a continuing desire for personal righteousness. 
Imagine the epitaph written about a man with this virtue. “What a good man he is in life.” Of course, we would find it hard to be described as good ourselves because the only One “good” is Jesus Himself. This characteristic of righteousness is modeled to the fullest by Christ Himself. Nevertheless, the intensity, all consuming, passionate longing for His righteousness over anything else of this world is what brings satisfaction and true fulfillment.
When we examine this beatitude further we can see beyond the demand and see the value obtained when you pursue this virtue. One element is when a man obtains righteousness through Christ, but the second value is the man who pursues this virtue. He is the man who is on the hunt with all his senses tuned into capturing its prey. The Greek grammar in this passage also brings out the element of this hunger and thirst. The genitive case in the English is expressed by the word “of” and “of the man” is in the genitive case of the text.. An example would be “I hunger for of bread.” It was some bread, a part of bread, not the whole loaf. Another would be “I thirst for of water.” It was some water, a drink of water, not all the water in the tank. Righteousness is in the direct accusative, and not in the normal genitive. So the verbs hungering and thirsting take on the accusative. The meaning of hungering and thirsting is for the whole thing. Hungering for bread in the accusative is you want the whole loaf. Thirsting for water is you want all that is in tank. Blessed are those who hunger and thirst for the whole of righteousness, for complete righteousness, for total righteousness, for all righteousness.
In the Antarctic summer of 1908-9, Sir Ernest Shackleton and three companions attempted to travel to the South Pole from their winter quarters. They set off with four ponies to help carry the load. Weeks later, their ponies dead, rations all but exhausted, they turned back toward their base, their goal not accomplished.
Altogether, they trekked 127 days. On the return journey, as Shackleton records in The Heart of the Antarctic, the time was spent talking about food — elaborate feasts, gourmet delights, sumptuous menus. As they staggered along, suffering from dysentery, not knowing whether they would survive, every waking hour was occupied with thoughts of eating. “Blessed are those who hunger and thirst for RIGHTEOUSNESS.” Jesus intends for our quest for righteousness to be of this intensity.
“Not until I went into the churches of America and heard her pulpits aflame with righteousness did I understand the secret of her genius and power. America is great because she is good, and if America ever ceases to be good, she will cease to be great.” – Tocqueville