Spoilers below, for the 3 people on the planet who have not read Harry Potter.
At the end of Harry Potter and the Goblet of Fire, we have the climactic scene of Voldemort’s reconstitution, and his attempted killing of Harry Potter. This is the moment where the series takes its darker turn: a fellow student is dead, the main villain, who has been a mere shadow in the distance, has regained his powers, and Harry himself is on the brink of being another victim.
During the showdown, when Harry’s wand connects with Voldemort’s, and the specters of Voldemort’s victims start appearing, we are prepared for the moment when Harry’s parents will show up. We expect it.
But they do not appear together. First, his mother, and though she is the one mentioned previously, by Voldemort himself, as the sacrifice that protected Harry from death, Lily Potter’s job in this scene is to act as a herald for someone else.
Every other ghost gives a word of encouragement and so does Lily, but her encouragement takes on a different tone. She says, “Your father is coming. He wants to see you…it will be all right…hold on.”
And we, as readers, feel the weight of James Potter’s arrival just as much as Harry. Something important is happening. A father talking to his son for the first time, and a son taking heed. A father, attempting to save the life of his only son…again. In the graveyard where Voldemort has just desecrated his own father’s grave, Harry listens to the voice of his own father, and obeys.
This is one of Rowling’s best scenes, and it makes you wish she had wielded this kind of craftsmanship over the entire book.
A father’s presence is felt. His absence is felt even more. Rowling understood this, and she rolls out the red carpet for James Potter.
For a father to have this sort of gravitas, however, he must take responsibility for those under his care. While Lily rightly gets the praise and credit for her sacrifice, it is James who was the first lay down his life, trying to protect his family.
And so, though just an ephemeral ghost, James Potter’s arrival makes a deep impact.
Dumbledore will mumble something later on about echoes and shadows, but we readers know the truth: those were the souls of the dead. And the last to appear was the soul of James Potter, a father who still loved his son.