Their friendly results in general tell us a lot about how prepared they are. Yes, they aren't ready obviously. Am I surprised with that? No, of course. 
There is a small amount of time like 2 weeks left for new season to start. They still don't know what they are doing in the transfer market. For example they signed Filip Jorgensen. Why? Was there a need for an extra goalkeeper?
You have Sanchez, Petrovic, Kepa who can be used as starters. Now you have brought another goalkeeper who would surely like to have a good level of playing time. How can Enzo Maresca deal with all of them without making any of them unhappy? 
There is a small amount of time like 2 weeks left for new season to start. They still don't know what they are doing in the transfer market. For example they signed Filip Jorgensen. Why? Was there a need for an extra goalkeeper?
You have Sanchez, Petrovic, Kepa who can be used as starters. Now you have brought another goalkeeper who would surely like to have a good level of playing time. How can Enzo Maresca deal with all of them without making any of them unhappy? I won't come here saying I know him too well or saying I've watched him but he will be an upgrade to them all.
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Football has really evolved and for you to catch up with other clubs you need to get players who are good examples of a modern day player or goalkeeper.
Filip Jorgensen is a modern day goalkeeper, when it comes to making saves, passing skills with both legs as a goalkeeper, ball distribution and confidence, he got that. You can go see his highlights for Villarreal last season.
Sanchez is a flop, do I need to tell you that again? Petrovic is not a good ball playing goalkeeper so he cannot thrive under the new manager. I'm afraid he needs to find a new club and the same with Arizabalaga Kepa. Real Madrid wants him anyways. I don't know how this ends for him.
As for how they play, Chelsea will improve, I feel like they'll have a good start with this manager. Go tale a look at the history they had with Italians. Enzo Maresca will also be another successful Italian manager managing Chelsea I'm certain. He needs to solve the defense anyways.