1 Gale will become Max Devlin
Gale will become the future Max Devlin Mr.Landau was talking about. Gale will use the CD she got to make money and then she will use the money to construct a perfect time machine in 2029.
2 The killer is future Jim
Jim will eventually become a killer as a result of realizing that his coworkers hated him and that the CD can help him become rich. For a short while, Jim thought he could become Max Devlin but Gale prevented that when she killed him.
3 The CD is a fortune
The CD that Mr Landau had contained detailed stock prices for stocks in the future. The person who has the CD could make a very large amount of money because of knowing about the future price of stocks for many years to come.
4 The future couldn't be changed
In many parts of the movie, attempts to change the future were done but all of them failed. According to the movie, fate cannot be changed and so the same scenario happens no matter what they do. (See The Ninth Gate (1999) Movie Explained)
5 Mr. Landau acquired the CD
Mr. Landau broke into a secret facility in a town called destiny and acquired the CD which belonged to Max Devlin (or future Gale).
6 Jim had to kill his friends
Jim had to kill his friends to prevent them from changing the events so that he can become Max Devlin. Jim failed to do so because he didn't know that fate can't be changed. He thought he could be Max Devlin but his plan failed. (See The Devil’s Candy (2017) Movie Explained)
7 Jim went back to kill Randy
In the beginning of the movie, we see Randy trying to warn the people not to come because he saw what will happen in the future. Future Jim returned back and killed him to continue the events.