This grammar pattern is used with a verb to show some background of the second clause. Also, the contents before ‘-는데, -은데/ㄴ데, -인데’ draw out the attention to what comes after the discourse.
● 이 분은 우리 선생님인데 친절한 분이세요. (This is my teacher, and she is kind.)
● 이 가방은 지난주에 샀는데 아주 마음에 들어요. (I bought this bag last week, and I like it.)