+0
There were times when the patient’s life could not be saved, but the ER physician maintained composure and performed his task. I was deeply inspired by ER physicians’ ability to treat patients, even under high pressure situations. This was the moment when I realized that becoming a physician who preserved lives was the path for me.
+0
Hello, clubwestpua - and welcome to English Forums.

There were times when the patient’s life could not be saved, but the ER physician maintained his composure and performed his task. I was deeply inspired by the ER physicians’ ability to treat patients under pressure, and I realized then that becoming a physician was the path for me.
Comments  
Teachers: We supply a list of EFL job vacancies
thank you very much, so if I want to include "who preserved lives" within the last sentence, do I need to add commas like this?

I realized then that becoming a physician, who preserved lives, was the path for me
Yes, but I wouldn't include it: it insults the reader's intelligence.