This is the 738th most frequent Japanese word.
目指し
"目指し" (mezashi) means "aim" or "goal."
The word "目指して" here is used to indicate the goal or aim of becoming a doctor.
彼は医者を目指して一生懸命勉強している。
He is studying hard aiming to become a doctor.
The word "目指して" in this sentence shows the intent-directed effort towards achieving success.
彼女は成功を目指して努力している。
She is striving aiming at success.
Here, "目指し" employs the meaning of working towards a preferred or chosen objective, which is the better future.