Listening to the khutbah - adab and reward
The Prophet ﷺ stressed silence so strongly that even hushing someone else counts as idle talk:
"If you say to your companion 'be quiet' while the imam is delivering the khutbah on Friday, you have engaged in idle talk (laghw)." - Sahih al-Bukhari 934, Sahih Muslim 851
And the one who comes, listens and stays silent receives a tremendous reward:
"Whoever performs wudu well, then comes to the Friday prayer, listens and stays silent, is forgiven what is between it and the next Friday, and three days more." - Sahih Muslim 857