Initially, Andrew is a bright, enthusiastic young doctor fresh out of medical school, full of idealism and a desire to serve the community. His time in Blaenelly shapes him drastically:
* Loss of Naiveté: Blaenelly shatters his rosy view of medical practice. He confronts the harsh realities of poverty, inadequate resources, and the compromised ethics of some of his colleagues. He witnesses firsthand how social inequalities impact health and how the profit motive can overshadow patient well-being. His initial belief in the inherent goodness of the medical profession is challenged.
* Development of Critical Thinking: He learns to question authority and the established practices, particularly the cynical, profit-driven approach of Dr. Lennox. He develops his own moral compass, independent of the pressures and compromises he observes around him. This is crucial to his later actions.
* Exposure to the Human Cost of Neglect: He encounters suffering and death on a scale he never anticipated, leading to personal growth and a greater sense of responsibility towards his patients. This experience makes him more empathetic and compassionate.
* Personal Growth through Struggle: The challenges and frustrations of his work in Blaenelly, combined with his personal struggles (his marriage, financial difficulties), force him to grow up and become more resilient. He learns to cope with adversity and to stand up for what he believes in, even at a personal cost.
* Finding his Voice: While initially quiet and unsure, his experiences empower him to speak out against injustice and unethical practices. He begins to act on his principles, demonstrating increasing independence and courage. This sets the stage for his departure from Blaenelly and his later journey in London.
In short, Blaenelly doesn't just change Andrew Manson's professional life; it fundamentally alters his personal values and strengthens his resolve to practice medicine ethically, even when facing obstacles and considerable pressure. It becomes the crucible in which he is forged into the more principled and courageous doctor he becomes later in the novel.