Having at last escaped the evil John Aycliffe, Crispin and Bear leave Great Wexly to the sound of their own music and singing. Having defeated Aycliffe, Crispin is full of joy and declares that he has found both his soul and his name. He says, "And my name—I knew with all my heart—was Crispin" (58.46). This is a big deal for a boy who has spent thirteen years thinking he isn't even worthy of a name greater than "Asta's son" and who recently discovered that the father he is named for was kind of a jerk.
Taking the name Crispin as his own indicates two major points: He now believes himself worthy of a name—his self-esteem has come a long way since he left Stromford—and he's able to separate himself from the father who never wanted him enough, to the point that it doesn't bother him any longer that they share a name. Crispin is his own man, a free man who will not be bound by who his father was.