sermonize
verb [ I ] (UK usually sermonise) uk/ˈsɜː.mə.naɪz/ us/ˈsɝː.mə.naɪz/
disapproving长篇大论地说教
to give a long talk to people, telling them how they should behave in order to be better people
My grandmother's all right until she starts sermonizing and then she's unbearable. 我祖母人很好，可是一旦她开始长篇大论地说教，就让人难以忍受了。
Synonym: moralize