Previously, when you received a Notification it was a standalone update in your feed, so you had to open the actual Card if you wanted more context before responding. We quickly realized this wasn’t the most effective way to manage your updates so we’ve replaced Notifications with Threads.
When you receive an update in Threads, you will see the entire conversation related to that update - i.e. all of the comments associated with a Card or all of the comments associated with a specific Checklist item.
Find out more about managing your Threads here.