Koine (Biblical) Greek Grammar

“The teacher gave the student her friend’s book.”
Nominative – subject (“the teacher”)
Genitive – possession, relationship, part of (“her friend”)
Dative – indirect object (“the student”)
Accusative – direct object (“the book”)

"When the object of hungering and thirsting in Greek takes the accusative instead of the genitive, the meaning is that the hunger and the thirst are for the whole thing. To say I hunger for bread in the accusative means I want the whole loaf. To say I thirst for water in the accusative means I want the whole pitcher.” - William Barclay

“These hungry ones desire the whole thing, complete righteousness, rather than a part of it. The phrase breathes whole-heartedness. If we have a passionate desire to be right with God and stay that way, he is going to meet that desire to the full…” - The Bible Speaks Today Commentary

“Since that is so, this beatitude is in reality a question and a challenge. In effect, it demands: ‘How much do you want goodness? Do you want it as much as a starving person wants food, and as much as someone dying of thirst wants water?’ How intense is our desire for goodness? Most people have an instinctive desire for goodness, but that desire is wistful and vague rather than sharp and intense; and when the moment of decision comes, they are not prepared to make the effort and the sacrifice which real goodness demands.”

- William Barclay