Commentary for Genesis 37:6

שמעו נא החלום הזה, not only did he tell them his dream, as something by the way, but he invited them to listen to him tell it by saying שמעו נא “please pay attention!” This could not fail to intensify the hostility of his brothers, as we see immediately by their reaction: “do you plan to rule over us?!”

שמעו נא החלום, please listen to the dream, etc. He had to add the word נא, please, because at first they had refused to listen.

ויאמר אליהם: שמעו נא, he said to them: “please listen (to my dream).” His reason for telling them of his dream was to explain to them that his being destined for greatness was not due to the way his father preferred him, but seemed to be a destiny decreed by heaven.