Why is the kiss by Johnnie Taylor the “end of her childhood

Nanny is convinced that Janie's kiss has brought her into womanhood. She slaps Janie for her indiscretion, and tells her that she must get married to Logan Killicks. Janie objects, saying that Logan is ugly and old. But Nanny repeats that Janie must get married to someone who will keep her safe and protected. Nanny reiterates that she just wants to protect Janie from the burden of being a black woman.