Why cutting back and fourth between conversations in chapter three.

In Chapter 3 Huxley introduces the main social issues and themes of the story. The various conversations serve as a platform to convey these ideas to the reader. The Director launches into an explanation of the "lab". Mustapha Mond interrupts him with an explanation of the old nuclear family and its limitations. This combined with other characters' reactions provide a suitable spring board into the main themes and conflicts of the story.