Read the following article and answer the question.

They came first for the Communists , and I did n't speak up because I was n't a Communist . Then they came for the Jews , and I did n't speak up because I was n't a Jew . Then they came for the trade unionists , and I did n't speak up because I was n't a trade unionist . Then they came for the Catholics , and I did n't speak up because I was a Protestant .

What is the purpose of the post ?
To teach history