The force Jack puts into the words when he says it.
You can seriously just tell how angry and hurt he is here, even though he manages to reign it in a little bit in the next few sentences. The one who created him, who gave him life and a name and then ignored him for 300 years, has finally said something about him.
And it wasn’t even to him.
He was talking to the Guardians just a few seconds ago. But his finale, this angry statement spoken in nothing short of pent-up frustration, is shouted up at the moon. All of his gestures are towards the moon. His words, his narrowed glare, the throwing of his arm, the sharp step forward— All towards the Man in the Moon.
Because how dare he. How dare he ignore him for three centuries, and then give the answers he longed and begged and screamed for to someone else.