This is the 7290th most frequent Russian word.
вступил
"Entered" or "joined."
Here, 'вступила' means becoming a member of a group or organization.
Она вступила в клуб путешественников.
She joined the travelers' club.
In this context, 'вступил' denotes beginning an action or interaction, specifically an argument in this case.
После долгих колебаний, он вступил в пререкание.
After much hesitation, he engaged in an argument.
In this sentence, 'вступил' refers to the act of assuming a new professional role.