Learn Hardcore Japanese: sensei ha watasi ni syoukaizyou wo kaite kurete, mensetu de sore wo misemasita. - The teacher wrote a letter of introduction for me, and I showed it at the interview.

先生せんせい　は　私わたし　に　紹介状しょうかいじょう　を　書かいて　くれて、　面接めんせつ　で　それ　を　見みせました。sensei wa watashi ni shoukaijou o kaite kurete, mensetsu de sore o misemashita.

The teacher wrote a letter of introduction for me, and I showed it at the interview.

Breakdown of sensei wa watashi ni shoukaijou o kaite kurete, mensetsu de sore o misemashita.

はwa

topic particle

をo

direct object particle

Questions & Answers about sensei wa watashi ni shoukaijou o kaite kurete, mensetsu de sore o misemashita.

Why does the sentence use 先生は instead of 先生が at the beginning?

は marks the topic of the sentence, while が usually marks the grammatical subject in a neutral way.

先生は sets up “the teacher” as what we’re talking about for this sentence (or paragraph).
Using 先生が would put more emphasis on who did the action, like: “It was the teacher who wrote it,” which feels more contrastive or focused.

In this sentence, the main point is the situation (the teacher wrote me a recommendation and I showed it), not specifically contrasting the teacher with someone else. So 先生は is natural as a topic marker:
先生は (as for the teacher), 私に紹介状を書いてくれて、…

What is the role of に in 私に紹介状を書いて?

The に after 私 marks the indirect object or beneficiary of the action.

私に紹介状を書く = “to write a letter of recommendation for me / to me.”

Here, 私に shows that the action of writing the recommendation is directed toward you, or done for your benefit. In English this becomes “wrote a letter of recommendation for me.”

What does 書いてくれて mean exactly, and how is it different from just 書いて?