I'm trying to get this paragraph
Remembering what it was like not to be who we are now is vital to our growth and integrity. The best professors remain friends with their past. They remember what it was like not to know about their special topic – and so don’t talk over the heads of their students.
- what "remain friends" means?
- their past = the best professors' past?
- The last sentence = They don't talk over their students' head because they remember the period they also did not know about many topics?