What is the theme in The Three Musketeers by Alexandre Dumas, pere?

The quest is the main theme of the book. The book begins with a quest: young d'Artagnan sets out for Paris to seek his fortune. Like many heroes of quests, he is of noble birth but humble circumstance and must rely on his own wits and talent to rise to the level of his destiny. He yearns to be a Musketeer but must first prove himself worthy of the position. Aided by his father's friend, de Treville, he becomes a guard, and because of his curiosity, initiative, and pride, he is drawn into the center of a web of intrigue that eventually allows him to prove his worth and gain success as a Musketeer.