Sullivan is the teacher Jonathan Livingston Seagull meets when he enters a higher plane of existence in the second part of the novel. Sullivan is a wise mentor who pushes Jonathan not to limit himself but to fly higher and higher. He also explains to Jonathan that he arrived in this new, heavenly plane because of his strivings in his former world. Unlike most other seagulls—for whom flight is a means to the end of finding food—Jonathan loved flight for the gift it was, regardless of whether or not it led to a meal. He asked the kind of probing questions that made him an outcast in his society. These traits made him the rare, one-in-a-million bird that could ascend to a higher plane of existence. As Sullivan tells Jonathan,

We choose our next world through what we learn in this one.

Sullivan, however, teaches Jonathan an even more important lesson. He tells Jonathan that to truly ascend to the highest levels, he has to let go of the bitterness and lack of forgiveness he harbors against those who misunderstood him in his former life. He needs to learn to love those who hated him. In fact, the Christlike Jonathan ends up returning to his former life to teach those he left behind.