“Summary of the FAA’s Review of the Boeing 737 MAX”
https://www.faa.gov/foia/electronic_reading_room/boeing_read...
“The 737 MAX was designed to handle and feel the same to the pilot as the 737 NG. Without the MCAS function, in some small areas of the flight envelope — such as approaching a stall and during higher g-force maneuvering — the new engines contribute to the control column feeling lighter in the 737 MAX than the regulations allow.”
The Flight envelope is unstable without MCAS.
“MCAS provides signals to move the horizontal stabilizer at elevated angles of attack to compensate for the aerodynamic effects of the 737 MAX’s larger and more forward-located engines, resulting in the required column feel to the pilot.”
The plane pitches nose-up under high acceleration.