Golden Lines are sentences that "speak" to you while you read. Here is where I found the great Golden Line description below. When I read I look for my favorite lines or quotes. You'll find these in my book summaries.
This strategy engages readers to look for a specific point that “speaks” to them. “Golden Lines” are Powerful quotes that automatically provide interesting discussion material. Many students find it much easier to select something the author said than to come up with their own reactions. Therefore, Golden Lines are an easy and effective strategy for student to determine important ideas, make connections, and visualize during reading.
Here's a document you can refer to when using Golden Lines with students.