Final answer:
Calvin is asked to join Meg and Charles Wallace on their journey to offer balance, emotional support, and to experience his own personal growth.
Step-by-step explanation:
The query about why Calvin is asked to go on the journey with Meg and Charles Wallace is related to the novel 'A Wrinkle in Time' by Madeleine L'Engle. The novel doesn't explicitly state why Calvin joins the journey, but we can infer that his presence is necessary for several reasons. Firstly, Calvin brings balance to the trio with his social ease and athletic prowess, complementing Meg's intellectual strength and Charles Wallace's unique abilities. Moreover, Calvin's character provides emotional support for Meg and he acts as a mediator when tensions arise. Additionally, Calvin's own personal growth and discovery of his strengths form a vital part of the story's theme of self-acceptance and understanding one's role in the universe.