Why had Lambert Strether been sent to Paris in The Ambassadors?

In Henry James's novel The Ambassadors, Lambert Strether is sent to Paris by his wealthy, widowed fiancée, Mrs. Newsome, to act as an "ambassador" on her behalf.12

Mrs. Newsome had become deeply disturbed by reports regarding the love life of her son, Chadwick, who had been living abroad in Paris for some time. She tasked Strether with the mission of engineering Chadwick’s return to their home in a Massachusetts industrial town, effectively bringing him back under his mother’s sphere of influence.12

Ultimately, the mission fails to go as planned; upon arriving in Paris, Strether finds that Chadwick has matured and improved, and he himself becomes captivated by the social and aesthetic attractions of Parisian life, eventually advising the young man to remain abroad.12